Lighting device

ABSTRACT

A lighting device includes light emitting element groups (HSB) including a light emitting element group (HS2) that emits light when being applied with a voltage at a light emission reference voltage (VH2), and a light emitting element group (HS12) that emits light when being applied with a light emission reference voltage (VH12) higher than the light emission reference voltage (VH2), the light emitting element groups (HSB) emitting light when being applied with a voltage equal to or higher than a light emission reference voltage (VHa); a semiconductor chip (IC1) including a light emission control unit (HC1) arranged to perform light emission control to cause light emission of a light emitting element group (HS) if a drive voltage (Vk) is higher than the light emission reference voltage (VHa), and to perform light emission stop control to stop the light emission if the drive voltage (Vk) is lower than the same; and a semiconductor chip (IC2) including a light emission control unit (HC2) arranged to perform light emission control to cause light emission of a light emitting element group (HSa) if the drive voltage (Vk) is higher than the light emission reference voltage (VHa), and to perform light emission stop control to turn off the emitting element group (HSa) if the drive voltage (Vk) is lower than the same.

TECHNICAL FIELD

The present invention relates to a lighting device constituted of aplurality of light emitting elements.

BACKGROUND ART

Recent years, along with diversification of design of lighting devices,as disclosed in Patent Document 1 or Patent Document 2, there is known alighting device in which a plurality of light emitting element groupsconnected in parallel to each other with respect to a power supplycircuit include different numbers of light emitting elements.

List of Citations

PATENT LITERATURE

Patent Document 1: JP-A-2010-225413

Patent Document 2: JP-A-2008-77944

SUMMARY OF THE INVENTION Technical Problem

In the conventional lighting device as described above, the lightemitting element groups may have different light emission referencevoltages necessary for light emission. For example, at rising or fallingof the power supply to drive the lighting device, if a voltage suppliedfrom the power supply circuit does not have a sufficient level, turn-onand turn-off timings of the light emitting elements in the lightemitting element groups may be varied. If turn-on and turn-off timingsof the light emitting elements in the light emitting element groups ofthe lighting device are varied, fine view may be impaired. In addition,when the lighting device is used as an in-vehicle exterior lamp, forexample, it may be woolly lighting and may cause an accident, which is aproblem.

It is an object of the present invention to provide a lighting devicethat prevents a variation in turn-on and turn-off timings of a pluralityof light emitting element groups connected in parallel to each otherwith respect to a power supply circuit.

Means for Solving the Problem

A lighting device according to the present invention includes a powersupply circuit arranged to supply a drive voltage; light emittingelement groups including a first light emitting element group having aplurality of first light emitting elements connected in series, arrangedto emit light by a first light emission current flowing when beingapplied with a first light emission voltage based on the drive voltage,at a first light emission reference voltage or higher, and a secondlight emitting element group having a plurality of a second lightemitting elements connected in series, arranged to emit light by asecond light emission current flowing when being applied with a secondlight emission voltage based on the drive voltage, at a second lightemission reference voltage higher than the first light emissionreference voltage, the light emitting element groups emitting light whenbeing applied with a light emission voltage equal to or higher than alight emission reference voltage based on the second light emissionreference voltage; a first semiconductor chip including a first lightemission control unit arranged to detect a magnitude relationshipbetween the drive voltage and the light emission reference voltage, toperform light emission control to cause light emission of the lightemitting element group if the drive voltage is higher than the lightemission reference voltage, and to perform light emission stop controlto stop light emission of the light emitting element group if the drivevoltage is lower than the light emission reference voltage, the firstsemiconductor chip being connected to the first light emitting elementgroup; and a second semiconductor chip including a second light emissioncontrol unit arranged to detect a magnitude relationship between thedrive voltage and the light emission reference voltage, to perform lightemission control to cause light emission of the light emitting elementgroup if the drive voltage is higher than the light emission referencevoltage, and to perform light emission stop control to stop lightemission of the light emitting element group if the drive voltage islower than the light emission reference voltage, the secondsemiconductor chip being connected to the first semiconductor chip andthe second light emitting element group.

In addition, a lighting device according to the present inventionincludes light emitting element groups including a first light emittingelement group having a plurality of first light emitting elementsconnected in series, arranged to emit light by a first light emissioncurrent flowing when being applied with a first light emission voltagebased on the drive voltage, at a first light emission reference voltageor higher, and a second light emitting element group having a pluralityof a second light emitting elements connected in series, arranged toemit light by a second light emission current flowing when being appliedwith a second light emission voltage based on the drive voltage, at asecond light emission reference voltage higher than the first lightemission reference voltage, the light emitting element groups emittinglight when being applied with a light emission voltage equal to orhigher than a light emission reference voltage based on the second lightemission reference voltage; and a light emission control unit arrangedto detect a magnitude relationship between the drive voltage and thelight emission reference voltage, to perform light emission control tocause light emission of the light emitting element group if the drivevoltage is higher than the light emission reference voltage, and toperform light emission stop control to stop light emission of the lightemitting element group if the drive voltage is lower than the lightemission reference voltage.

Advantageous Effects of the Invention

With the lighting device according to the present invention, it ispossible to prevent a variation in turn-on and turn-off timings in aplurality of light emitting element groups connected in parallel to eachother with respect to a power supply circuit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a lighting device 10 according to afirst embodiment of the present invention.

FIGS. 2A to 2E are diagrams illustrating transitions of signal waveformsfrom rising to falling of a power supply to drive the lighting device10.

FIG. 3 is a diagram illustrating a lighting device 10 a according to afirst variation of the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a lighting device 10 b according to asecond variation of the first embodiment of the present invention.

FIG. 5 is a diagram illustrating a lighting device 20 according to asecond embodiment of the present invention.

FIGS. 6A to 6E are diagrams illustrating transitions of signal waveformsfrom rising to falling of a power supply to drive the lighting device20.

FIG. 7 is a diagram illustrating a lighting device 20 a according to afirst variation of the second embodiment of the present invention.

FIG. 8 is a diagram illustrating a lighting device 30 according to athird embodiment of the present invention.

FIGS. 9A to 9E are diagrams illustrating transitions of signal waveformsfrom rising to falling of a power supply to drive the lighting device30.

FIG. 10 is a diagram illustrating a lighting device 30 a according to afirst variation of the third embodiment of the present invention.

FIG. 11 is a diagram illustrating a lighting device 30 b according to asecond variation of the third embodiment of the present invention.

FIG. 12 is a diagram illustrating a lighting device 30 c according to athird variation of the third embodiment of the present invention.

FIG. 13 is a diagram illustrating a lighting device 40 according to afourth embodiment of the present invention.

FIG. 14 is a diagram illustrating a lighting device 40 a according to afirst variation of the fourth embodiment of the present invention.

FIG. 15 is a diagram illustrating a lighting device 40 b according to asecond variation of the fourth embodiment of the present invention.

FIG. 16 is a diagram illustrating a lighting device 40 c according to athird variation of the fourth embodiment of the present invention.

FIG. 17 is a diagram illustrating a lighting device 40 d according to afourth variation of the fourth embodiment of the present invention.

FIG. 18 is a diagram illustrating a lighting device 40 e according to afifth variation of the fourth embodiment of the present invention.

FIG. 19 is a diagram illustrating a lighting device 40 f according to asixth variation of the fourth embodiment of the present invention.

FIG. 20 is a diagram illustrating a lighting device 40 g according to aseventh variation of the fourth embodiment of the present invention.

FIG. 21 is a diagram illustrating a lighting device 40 h according to aneighth variation of the fourth embodiment of the present invention.

FIG. 22 is a diagram illustrating a lighting device 40 i according to aninth variation of the fourth embodiment of the present invention.

FIG. 23 is a diagram illustrating a lighting device 40 j according to atenth variation of the fourth embodiment of the present invention.

FIG. 24 is a diagram illustrating a lighting device 40 k according to aneleventh variation of the fourth embodiment of the present invention.

FIG. 25 is a diagram illustrating a lighting device 50 according to afifth embodiment of the present invention.

FIG. 26 is a diagram illustrating a lighting device 50 a according to afirst variation of the fifth embodiment of the present invention.

FIG. 27 is a diagram illustrating a lighting device 50 b according to asecond variation of the fifth embodiment of the present invention.

FIG. 28 is a diagram illustrating a lighting device 50 c according to athird variation of the fifth embodiment of the present invention.

FIG. 29 is a diagram illustrating a lighting device 50 d according to afourth variation of the fifth embodiment of the present invention.

FIG. 30 is a diagram illustrating a lighting device 50 e according to afifth variation of the fifth embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, with reference to the drawings, embodiments of the presentinvention are described. Note that numeric values, circuits, and thelike can be appropriately selected within the scope of the presentinvention without deviating from the spirit thereof.

First Embodiment

FIG. 1 is a diagram illustrating a lighting device 10 according to afirst embodiment of the present invention. The lighting device 10includes a power supply circuit VS, light emitting element groups HS,and a light emission control unit HC. The lighting device 10 is used asan in-vehicle exterior lamp such as a head lamp, a winker, a hazardlamp, or a brake lamp, but this is not a limitation.

The power supply circuit VS outputs a drive voltage Vk of 12 V, forexample. In addition, the power supply circuit VS can supply a drivecurrent Ik having a current value corresponding to a load to which thedrive voltage Vk is supplied.

The light emitting element groups HS include a light emitting elementgroup HS1, and a light emitting element group HS2. The light emittingelement groups HS are the load to which the drive voltage Vk issupplied.

The light emitting element group HS1 includes a plurality of lightemitting elements HS1 a connected in series, and a resistor element Rh1.The light emitting element HS1 a is a light emitting diode (LED) and isa self light emitting element. The cathode of the light emitting elementHS1 a as one terminal of the light emitting element group HS1 isconnected to one terminal of the resistor element Rh1. The otherterminal of the resistor element Rh1 is connected to a power supply VSSas a first power supply having a potential such as 0 V lower than thedrive voltage Vk. Note that the light emitting element HS1 a is notlimited to an LED but may be a general organic electro luminescence (EL)element such as a light emitting polymer as a self light emittingelement.

The light emitting element group HS1 emits light by a light emissioncurrent Ih1 flowing in each of the light emitting elements HS1 a, when alight emission voltage Vh1 equal to or higher than a light emissionreference voltage VH1 based on the drive voltage Vk is applied to theanode of the light emitting element HS1 a as the other terminal ofitself. Note that a current value of the light emission current Ih1 isdetermined based on a resistance value of the resistor element Rh1. Inaddition, each of the light emitting elements HS1 a has an internalresistance, and a forward voltage of one light emitting element HS1 a issupposed to be 2 V, for example.

Here, the light emission reference voltage VH1 for the light emittingelement group HS1 to emit light in this embodiment is 6 V, for example,because the light emitting element group HS1 includes three lightemitting elements HS1 a connected in series, each of which has a forwardvoltage of 2 V. In other words, in order that the light emitting elementgroup HS1 emits light, the light emission voltage Vh1 applied to theanode of the light emitting element HS1 a on the other terminal must be6 V or higher.

Here, “the anode of the light emitting element HS1 a as the otherterminal of the light emitting element group HS1” is referred to as anode Nh1, and “the cathode of the light emitting element HS1 a as theone terminal of the light emitting element group HS1” is referred to asa node Nh1 a. In addition, “the light emission current Ih1 flowing ineach of the light emitting elements HS1 a” is referred to as “the lightemission current Ih1 flowing in the light emitting element group HS1”.

The light emitting element group HS2 includes a plurality of lightemitting elements HS2 a connected in series, and a resistor element Rh2.The light emitting element HS2 a is a light emitting diode (LED) and isa self light emitting element. The cathode of the light emitting elementHS2 a as one terminal of the light emitting element group HS2 isconnected to one terminal of the resistor element Rh2. The otherterminal of the resistor element Rh2 is connected to the power supplyVSS. Note that the light emitting element HS2 a is not limited to an LEDbut may be a general organic electro luminescence (EL) element as a selflight emitting element, though this is not a limitation.

The light emitting element group HS2 emits light by a light emissioncurrent Ih2 flowing in each of the light emitting elements HS2 a, when alight emission voltage Vh2 equal to or higher than a light emissionreference voltage VH2 higher than the light emission reference voltageVH1 based on the drive voltage Vk is applied to the anode of the lightemitting element HS2 a as the other terminal of itself. Note that acurrent value of the light emission current Ih2 is determined based on aresistance value of the resistor element Rh2. In addition, each of thelight emitting elements HS2 a has an internal resistance, and a forwardvoltage of one light emitting element HS2 a is supposed to be 2 V, forexample.

Here, the light emission reference voltage VH2 for the light emittingelement group HS2 to emit light in this embodiment is 8 V, for example,because the light emitting element group HS2 includes four lightemitting elements HS2 a connected in series, each of which has a forwardvoltage of 2 V. In other words, in order that the light emitting elementgroup HS2 emits light, the light emission voltage Vh2 applied to theanode of the light emitting element HS2 a on the other terminal must be8 V or higher.

Here, “the anode of the light emitting element HS2 a as the otherterminal of the light emitting element group HS2” is referred to as anode Nh2, and “the cathode of the light emitting element HS2 a as theone terminal of the light emitting element group HS2” is referred to asa node Nh2 a. In addition, “the light emission current Ih2 flowing ineach of the light emitting elements HS2 a” is referred to as “the lightemission current Ih2 flowing in the light emitting element group HS2”.

Here, in order that the light emitting element groups HS emits lightwithout an internal variation in this embodiment, i.e. in order that thelight emitting element group HS1 and the light emitting element group 2emit light simultaneously, a voltage higher than 8 V as the lightemission reference voltage VH2 must be applied to the light emittingelement groups HS as light emission voltage Vh, because the lightemission reference voltage VH2 is 8 V and is higher than the lightemission reference voltage VH1 that is 6 V. Here, the voltage for thelight emitting element groups HS to emit light without an internalvariation is referred to as light emission reference voltage VH. Thelight emitting element groups HS emits light when being applied with thelight emission voltage Vh higher than the light emission referencevoltage VH based on the light emission reference voltage VH2. Note that,in this embodiment, the light emission reference voltage VH is 8 V thatis the same as the light emission reference voltage VH2.

Note that this embodiment describes the example where the light emittingelement group HS2 includes more number of light emitting elements HS2 athan the number of the light emitting elements HS1 a disposed in thelight emitting element group HS1, but this is not a limitation. In otherwords, the lighting device 10 according to the present inventionachieves outstanding effects in cases where the light emission referencevoltage VH1 necessary for the light emitting element group HS1 to emitlight is different from the light emission reference voltage VH2necessary for the light emitting element group HS2 to emit light, and acase where the light emitting element group HS1 and the light emittingelement group HS2 have the same number of light emitting elements is notexcluded. In addition, in the same manner, each of the light emittingelements group HS1 and the light emitting element group HS2 may have asingle LED.

Here, if the light emitting element groups HS are applied with the lightemission voltage Vh, which is equal to or higher than the light emissionreference voltage VH1 and lower than or equal to the light emissionreference voltage VH2 without any control, the light emitting elementgroup HS1 emits light while the light emitting element group HS2 doesnot emit light. In addition, after that, when the light emission voltageVh becomes equal to or higher than the light emission reference voltageVH2 and is applied to the light emitting element groups HS, not only thelight emitting element group HS1 but also the light emitting elementgroup HS2 emits light. In other words, if the light emitting elementgroups HS are applied with the light emission voltage Vh lower than thereference voltage VH2, light emission timing is varied between the lightemitting element group HS1 and the light emitting element group HS2, andhence light emission of the entire light emitting element groups HS maybe fluctuated. In particular, when being used as an in-vehicle exteriorlamp, the fluctuation in light emission of the light emitting elementgroups may cause an accident. The lighting device 10 according to thepresent invention is aimed to prevent occurrence of such a problem.

The light emission control unit HC includes a comparing circuit CN and atransistor P1.

The comparing circuit CN includes a resistor element R1, a resistorelement R2, a reference power supply Ref1, and a comparator Cp1.

The resistor element R1 has one terminal connected to the power supplycircuit VS and has a resistance value of 400 ohms, for example. Here,connection node between the resistor element R1, i.e. the comparingcircuit CN and the power supply circuit VS is referred to as a node Nd1.The resistor element R2 has one terminal connected to the other terminalof the resistor element R1, and the other terminal connected to thepower supply VSS, and has a resistance value of 200 ohms, for example.Here, a connection node between the other terminal of the resistorelement R1 and the one terminal of the resistor element R2 is referredto as a node Nd2, and a potential at the node Nd2 is referred to as acomparison voltage Vc. The potential at the node Nd2 is a potentialobtained by dividing the drive voltage Vk by the resistor element R1 andthe resistor element R2.

The reference power supply Ref1 has one terminal connected to the powersupply VSS and generates a reference voltage Vref1 as a first referencevoltage. The reference voltage Vref1 is set to be equal to or higherthan a voltage value obtained by dividing the light emission referencevoltage VH by the resistor element R1 and the resistor element R2. Inother words, the reference voltage Vref1 is set based on the lightemission reference voltage VH. In this embodiment, the reference voltageVref1 is set to 3 V, for example, which is higher than 2.6 V obtained bydividing 8 V as the light emission reference voltage VH by 400 ohms ofthe resistor element R1 and 200 ohms of the resistor element R2.

The comparator Cp1 has an inverting terminal connected to the node Nd2,to which the comparison voltage Vc is input, and a noninverting terminalconnected to the other terminal of the reference power supply Ref1, towhich the reference voltage Vref1 is input. The comparator Cp1 comparesthe comparison voltage Vc with the reference voltage Vref1, and outputsa comparison result signal Vcr1 as the comparison result from an outputterminal. If the comparison voltage Vc is lower than the referencevoltage Vref1, the comparator Cp1 outputs the comparison result signalVcr1 of high level that is substantially the same voltage level as thedrive voltage Vk, for example. If the comparison voltage Vc is higherthan the reference voltage Vref1, the comparator Cp1 outputs thecomparison result signal Vcr1 of low level that is 0 V, for example.

As described above, the comparing circuit CN is connected to the powersupply circuit VS, determines whether the drive voltage Vk is higher orlower than a voltage based on the light emission reference voltage VH,and outputs the result as the comparison result signal Vcr1.

The transistor P1 is a PMOS transistor having a source terminal Sconnected to the power supply circuit VS, a drain terminal D connectedto the node Nh1 and the node Nh2, and a gate terminal G as a controlterminal connected to the output terminal of the comparator Cp1, i.e. tothe comparing circuit CN. The transistor P1 is on-off controlled by thecomparison result signal Vcr1, which is output from the comparingcircuit CN and input to the gate terminal G. In this way, light emissioncontrol and light emission stop control of the light emitting elementgroups HS are performed.

Note that the connection node among the drain terminal D of thetransistor P1, the node Nh1, and the node Nh2 is referred to as a nodeNd3. The light emitting element group HS1 and the light emitting elementgroup HS2 are connected in parallel to each other at the node Nd3 thatis the connection node to the drain terminal D of the transistor P1.

The transistor P1 is turned off when the comparison result signal Vcr1at high level output from the comparing circuit CN is input to the gateterminal G. In this case, the potential at the node Nd3 becomes 0 V, andthus the light emission voltage Vh becomes 0 V. Therefore, the lightemission voltage Vh1 applied to the light emitting element group HS1 is0 V, and the light emission current Ih1 flowing in the light emittingelement group HS1 is stopped to be 0 A, so that the light emittingelement group HS1 does not emit light. In addition, the light emissionvoltage Vh2 applied to the light emitting element group HS2 is 0 V, andthe light emission current Ih2 flowing in the light emitting elementgroup HS2 becomes 0 A, so that the light emitting element group HS2 doesnot emit light.

In addition, the transistor P1 is turned on when the low levelcomparison result signal Vcr1 output from the comparing circuit CN isinput to the gate terminal G. In this case, the potential at the nodeNd3 becomes 9 V or higher, for example, and the light emission voltageVh becomes 9 V or higher. Therefore, the light emitting element groupHS1 is applied with the light emission voltage Vh1 higher than 6 V asthe light emission reference voltage VH1, and the light emission currentIh1 flows so that the light emitting element group HS1 emits light. Inaddition, the light emitting element group HS2 is applied with the lightemission voltage Vh2 higher than 8 V as the light emission referencevoltage VH2, and the light emission current Ih2 flows so that the lightemitting element group HS2 emits light.

As described above, the light emission control unit HC detects amagnitude relationship between the drive voltage Vk and the lightemission reference voltage VH. If the drive voltage Vk is higher thanthe light emission reference voltage VH, the light emission control unitHC performs the light emission control to cause light emission of thelight emitting element groups HS by turning on the transistor P1 so thatthe light emission current Ih1 can be supplied to the light emittingelement group HS1 and the light emission current Ih2 can be supplied tothe light emitting element group HS2. If the drive voltage Vk is lowerthan the light emission reference voltage VH, the light emission controlunit HC performs the light emission stop control to stop light emissionof the light emitting element groups HS by turning off the transistor P1so that the light emission current Ih1 cannot be supplied to the lightemitting element group HS1 and the light emission current Ih2 cannot besupplied to the light emitting element group HS2. Therefore, thelighting device 10 according to this embodiment can cause as well asstop the light emission of the light emitting element group HS1 and thelight emitting element group HS2 at the same time.

FIGS. 2A to 2E are diagrams illustrating transitions of signal waveformsfrom rising to falling of a power supply to drive the lighting device10. FIG. 2A indicates the transition of the drive voltage Vk in temporalchange. FIG. 2B indicates a relationship between the transition of thecomparison voltage Vc and the reference voltage Vref1 in temporalchange. FIG. 2C indicates the transition of the comparison result signalVcr1 in temporal change. FIG. 2D indicates the transition of the lightemission voltage Vh in temporal change. FIG. 2E indicates thetransitions of the light emission current Ih1 and the light emissioncurrent Ih2 in temporal change. Note that, in each of FIGS. 2A to 2D,the vertical axis represents voltage V, and the horizontal axisrepresents time t. Further, in FIG. 2E, the vertical axis representscurrent I, and the horizontal axis represents time t. Further, timepoints t0 to t4 are common among FIGS. 2A to 2E.

At time point t0, drive of the power supply to drive the lighting device10 is started, and then a voltage level of the drive voltage Vk outputfrom the power supply circuit VS starts to increase. In this case, thecomparison voltage Vc obtained by dividing the drive voltage Vk is equalto or lower than 3 V as the reference voltage Vref1, and hence thecomparison result signal Vcr1 has substantially the same level as thedrive voltage Vk, so that the transistor P1 is in off state. Therefore,the light emission voltage Vh output from the transistor P1 is 0 V, sothat the light emission current Ih1 does not flow in the light emittingelement group HS1, and the light emission current Ih2 does not flow inthe light emitting element group HS2. In other words, at time point t0,the light emitting element groups HS are in off state.

At time point t1, when the drive voltage Vk becomes 9 V, the comparisonvoltage Vc becomes 3 V, and then becomes higher than 3 V as thereference voltage Vref1. Thus, the comparison result signal Vcr1 ischanged to low level. In this way, the transistor P1 is turned on sothat the light emission voltage Vh of approximately 9 V is output. Inthis case, because the light emission voltage Vh1 of approximately 9 Vapplied to the light emitting element group HS1 is higher than 6 V asthe light emission reference voltage VH1, the light emission current Ih1flows in the light emitting element group HS1 so that the light emittingelement group HS1 emits light. In addition, because the light emissionvoltage Vh2 of approximately 9 V applied to the light emitting elementgroup HS2 is higher than 8 V as the light emission reference voltageVH2, the light emission current Ih2 flows in the light emitting elementgroup HS2 so that the light emitting element group HS2 emits light. Inother words, the light emitting element group HS1 and the light emittingelement group HS2 emit light at the same timing without a variation.

At time point t2, when the drive of the power supply to drive thelighting device 10 is stopped, the drive voltage Vk starts to decrease.In this case, the light emission voltage Vh, the light emission currentIh1, and the light emission current Ih2, which are output from thetransistor P1 based on the comparison voltage Vc obtained by dividingthe drive voltage Vk, the light emission voltage Vh, and the drivevoltage Vk, also start to decrease.

At time point t3, when the decreasing drive voltage Vk becomes lowerthan 9 V, the comparison voltage Vc becomes lower than 3 V. In this way,the comparison result signal Vcr1 is changed to substantially the samelevel as the drive voltage Vk, the transistor P1 is turned off, andoutput of the light emission voltage Vh, the light emission current Ih1,and the light emission current Ih2 from the transistor P1 is stopped. Inthis way, supply of the light emission current Ih1 to the light emittingelement group HS1 and supply of the light emission current Ih2 to thelight emitting element group HS2 are stopped, and hence the lightemitting element group HS1 and the light emitting element group HS2 areturned off simultaneously. In this case, the transistor P1 is turned offat a time point when the light emission voltage Vh is higher than 8 V asthe light emission reference voltage VH2, it is avoided that the lightemitting element group HS1 and the light emitting element group HS2 areturned off at different timings with a variation.

At time point t4, the drive voltage Vk is decreased to 0 V. In this way,drive of the lighting device 10 is stopped.

As described above, in the lighting device 10 according to the firstembodiment of the present invention, the light emission control unit HCdetects a magnitude relationship between the drive voltage Vk and thelight emission reference voltage VH, performs light emission control tocause light emission of the light emitting element groups HS if thedrive voltage Vk is higher than the light emission reference voltage VH,and performs light emission stop control to stop light emission of thelight emitting element groups HS if the drive voltage Vk is lower thanthe light emission reference voltage VH. Therefore, it is possible toprevent a variation in timing of causing as well as stopping lightemission of the light emitting element group HS1 and the light emittingelement group HS2.

First Variation of First Embodiment

FIG. 3 is a diagram illustrating a lighting device 10 a according to afirst variation of the first embodiment of the present invention. Thelighting device 10 a includes the power supply circuit VS, the lightemitting element groups HS, the light emission control unit HC, adimming circuit LC1, and a dimming circuit LC2. The lighting device 10 aaccording to this variation is substantially different from the lightingdevice 10 illustrated in FIG. 1 in that the dimming circuit LC1 and thedimming circuit LC2 are further provided. Note that in the lightingdevice 10 a illustrated in FIG. 3, the same structure as in the lightingdevice 10 illustrated in FIG. 1 is denoted by the same numeral orsymbol, and description thereof is appropriately omitted.

The dimming circuit LC1 has one terminal connected to the node Nd3, i.e.the drain terminal D of the transistor P1 and the other terminalconnected to the node Nh1. In other words, the node Nh1 is connected tothe node Nd3 via the dimming circuit LC1. The dimming circuit LC1adjusts the light emission current Ih1 flowing in the light emittingelement group HS1 to have a predetermined current value, and thusadjusts light emission luminance of the light emitting element groupHS1. Here, when the transistor P1 is turned on, the drive voltage Vk issupplied to the dimming circuit LC1, and when the transistor P1 isturned off, supply of the drive voltage Vk to the dimming circuit LC1 isstopped.

Note that the dimming circuit LC1 may have a structure for adjustingamount of current to flow in the light emitting element group HS1 basedon a current value flowing in the light emitting element group HS1, ormay have a structure for causing a predetermined amount of current toflow in the light emitting element group HS1 by a PWM control, or othervarious structures can be adopted without limiting to these structures.In addition, because the lighting device 10 a is equipped with thedimming circuit LC1, it is possible to determine the current value ofthe light emission current Ih1 flowing in the light emitting elementgroup HS1 by the dimming circuit LC1, without the resistor element Rh1,or together with the resistor element Rh1. In addition, this embodimentdescribes the lighting device 10 a having the structure in which thedimming circuit LC1 is connected between the node Nd3 and the node Nh1as described above, but this is not the limitation, and the dimmingcircuit LC1 may be connected between the node Nh1 a and the power supplyVSS.

The dimming circuit LC2 has one terminal connected to the node Nd3, i.e.the drain terminal D of the transistor P1 and the other terminalconnected to the node Nh2. In other words, the node Nh2 is connected tothe node Nd3 via the dimming circuit LC2. In this way, the seriesconnection of the dimming circuit LC2 and the light emitting elementgroup HS2 is connected in parallel to the series connection of thedimming circuit LC1 and the light emitting element group HS1 at the nodeNd3. The dimming circuit LC2 adjusts the light emission current Ih2flowing in the light emitting element group HS2 to have a predeterminedcurrent value, and thus adjusts light emission luminance of the lightemitting element group HS2. Here, the drive voltage Vk is supplied tothe dimming circuit LC2 when the transistor P1 is turned on, and thesupply of the drive voltage Vk to the dimming circuit LC2 is stoppedwhen the transistor P1 is turned off.

Note that the dimming circuit LC2 may have a structure for adjustingamount of current to flow in the light emitting element group HS2 basedon a current value flowing in the light emitting element group HS2, ormay have a structure for causing a predetermined amount of current toflow in the light emitting element group HS2 by a PWM control, or othervarious structures can be adopted without limiting to these structures.In addition, because the lighting device 10 a is equipped with thedimming circuit LC2, it is possible to determine the current value ofthe light emission current Ih2 flowing in the light emitting elementgroup HS2 by the dimming circuit LC2, without the resistor element Rh2,or together with the resistor element Rh2. In addition, although thisembodiment describes the lighting device 10 a having the structure inwhich the dimming circuit LC2 is connected between the node Nd3 and thenode Nh2, this is not the limitation. The dimming circuit LC2 may beconnected between the node Nh2 a and the power supply VSS.

Second Variation of First Embodiment

FIG. 4 is a diagram illustrating a lighting device 10 b according to asecond variation of the first embodiment of the present invention. Thelighting device 10 b includes the power supply circuit VS, the lightemitting element groups HS, the dimming circuit LC1, the dimming circuitLC2, and a light emission control unit HCa. The lighting device 10 baccording to this variation is substantially different from the lightingdevice 10 a illustrated in FIG. 3 in that the light emission controlunit HCa is disposed instead of the light emission control unit HC. Notethat in the lighting device 10 b illustrated in FIG. 4, the samestructure as in the lighting device 10 illustrated in FIG. 1 or thelighting device 10 a illustrated in FIG. 3 is denoted by the samereference numeral or symbol, and description thereof is appropriatelyomitted.

The dimming circuit LC1 has one terminal connected to the node Nd1, andthus is connected to the power supply circuit VS. The dimming circuitLC1 adjusts the light emission current Ih1 flowing in the light emittingelement group HS1 to have a predetermined current value.

The dimming circuit LC2 has one terminal connected to the node Nd1, andthus is connected to the power supply circuit VS. The dimming circuitLC2 adjusts the light emission current Ih2 flowing in the light emittingelement group HS2 to have a predetermined current value.

The light emission control unit HCa includes the comparing circuit CN, atransistor P2, and a transistor P3.

The transistor P2 is a PMOS transistor, which has the source terminal Sconnected to the other terminal of the dimming circuit LC1, the drainterminal D connected to the node Nh1, and the gate terminal G as acontrol terminal connected to the comparing circuit CN. The transistorP2 is on-off controlled by the comparison result signal Vcr1, which isoutput from the comparing circuit CN and is input to the gate terminalG. In this way, light emission control and light emission stop controlof the light emitting element groups HS are performed. When thetransistor P2 is turned on, the drive voltage Vk, which is supplied fromthe power supply circuit VS to the source terminal S via the dimmingcircuit LC1, is output as the light emission voltage Vh1 from the drainterminal D.

When the comparison result signal Vcr1 having high level output from thecomparing circuit CN is input to the gate terminal G, the transistor P2is turned off. In this case, the light emission voltage Vh1 applied tothe light emitting element group HS1 becomes 0 V and the light emissioncurrent Ih1 supplied to the light emitting element group HS1 to flowbecomes 0 A. In other words, supply of the light emission current Ih1 tothe light emitting element group HS1 is stopped, and hence the lightemitting element group HS1 does not emit light. In addition, when thecomparison result signal Vcr1 having low level output from the comparingcircuit CN is input to the gate terminal G, the transistor P2 is turnedon. In this case, the light emission voltage Vh1 applied to the lightemitting element group HS1 becomes equal to or higher than 9 V, which ishigher than the light emission reference voltage VH1. Therefore, thelight emission voltage Vh1 higher than 6 V as the light emissionreference voltage VH1 is applied to the light emitting element group HS1so that the light emission current Ih1 is supplied to flow. In this way,the light emitting element group HS1 emits light.

The transistor P3 is a PMOS transistor, which has the source terminal Sconnected to the other terminal of the dimming circuit LC2, the drainterminal D connected to the node Nh2, and the gate terminal G as acontrol terminal connected to the comparing circuit CN. The transistorP3 is on-off controlled by the comparison result signal Vcr1, which isoutput from the comparing circuit CN and is input to the gate terminalG. In this way, light emission control and light emission stop controlof the light emitting element groups HS are performed. When thetransistor P3 is turned on, the drive voltage Vk supplied from the powersupply circuit VS to the source terminal S via the dimming circuit LC2is output as the light emission voltage Vh2 from the drain terminal D.

When the comparison result signal Vcr1 having high level output from thecomparing circuit CN is input to the gate terminal G, the transistor P3is turned off. In this case, the light emission voltage Vh2 applied tothe light emitting element group HS1 is 0 V, and the light emissioncurrent Ih2 supplied to the light emitting element group HS2 to flowbecomes 0 A. In other words, the supply of the light emission currentIh2 to the light emitting element group HS2 is stopped, and hence thelight emitting element group HS2 does not emit light. In addition, whenthe comparison result signal Vcr1 having low level output from thecomparing circuit CN is input to the gate terminal G, the transistor P3is turned on. In this case, the light emission voltage Vh2 applied tothe light emitting element group HS2 becomes 9 V or higher, which ishigher than the light emission reference voltage VH2. Therefore, thelight emission voltage Vh2 higher than 8 V as the light emissionreference voltage VH2 is applied to the light emitting element groupHS2, and hence the light emission current Ih2 is supplied to flow. Inthis way, the light emitting element group HS2 emits light.

Here, the series connection of the dimming circuit LC1 and the lightemitting element group HS1 is connected in parallel to the seriesconnection of the dimming circuit LC2 and the light emitting elementgroup HS2 with respect to the power supply circuit VS.

As described above, the light emission control unit HCa detects amagnitude relationship between the drive voltage Vk and the lightemission reference voltage VH. If the drive voltage Vk is higher thanthe light emission reference voltage VH, the light emission control unitHCa performs light emission control to cause light emission of the lightemitting element groups HS, by turning on the transistor P2 so that thelight emission current Ih1 can be supplied to the light emitting elementgroup HS1, and by turning on the transistor P3 so that the lightemission current Ih2 can be supplied to the light emitting element groupHS2. If the drive voltage Vk is lower than the light emission referencevoltage VH, the light emission control unit HCa performs light emissionstop control to stop light emission of the light emitting element groupsHS, by turning off the transistor P2 so that the light emission currentIh1 cannot be supplied to the light emitting element group HS1, and byturning off the transistor P3 so that the light emission current Ih2cannot be supplied to the light emitting element group HS2. Therefore,the lighting device 10 b according to this embodiment can cause as wellas stop the light emission of the light emitting element group HS1 andthe light emitting element group HS2 at the same time.

Note that the lighting device 10 b according to the second variation ofthe first embodiment of the present invention includes the transistor P2and the transistor P3 instead of the transistor P1 in the lightingdevice 10, and hence the light emission current Ih1 to flow in the lightemitting element group HS1 to cause light emission of the light emittingelement group HS1 and the light emission current Ih2 to flow in thelight emitting element group HS2 to cause light emission of the lightemitting element group HS2 can be supplied from the power supply circuitVS to the light emitting element group HS1 and the light emittingelement group HS2 through different transistors. Therefore, the currentconcentrated in the transistor P1 in the lighting device 10 can bedistributed between the transistor P2 and the transistor P3, and thuslocal heat concentration inside the lighting device can be prevented. Itis needless to say that this effect is enhanced in proportion to anincrease in the number of light emitting elements included in the lightemitting element groups HS or the number of the light emitting elementgroups connected in parallel to each other.

Second Embodiment

FIG. 5 is a diagram illustrating a lighting device 20 according to asecond embodiment of the present invention. The lighting device 20includes the power supply circuit VS, the light emitting element groupsHS, and a light emission control unit HCb. The lighting device 20according to this embodiment is substantially different from thelighting device 10 illustrated in FIG. 1 in that the light emissioncontrol unit HCb is disposed instead of the light emission control unitHC. Note that in the lighting device 20 illustrated in FIG. 5, the samestructure as in the lighting device 10 illustrated in FIG. 1 is denotedby the same numeral or symbol, and description thereof is appropriatelyomitted.

The light emitting element group HS1 has the other terminal connected tothe power supply circuit VS. In addition, the light emitting elementgroup HS2 has the other terminal connected to the power supply circuitVS. In this way, the light emitting elements HS1 a of the light emittingelement group HS1 and the light emitting elements HS2 a of the lightemitting element group HS2 are connected in parallel to each other withrespect to the power supply circuit VS. Note that the light emittingelement group HS1 in the lighting device 20 includes a resistor elementRh3 instead of the resistor element Rh1 in the lighting device 10, whichhas one terminal connected to the power supply circuit VS and the otherterminal connected to the node Nh1. The light emission current Ih1 isdetermined based on resistance values of the light emitting elements HS1a and the resistor element Rh3. In addition, the light emitting elementgroup HS2 in the lighting device 20 includes a resistor element Rh4instead of the resistor element Rh2 in the lighting device 10, which hasone terminal connected to the power supply circuit VS and the otherterminal connected to the node Nh2. The light emission current Ih2 isdetermined based on resistance values of the light emitting elements HS2a and the resistor element Rh4. In addition, the resistance value of theresistor element Rh3 is larger than the resistance value of the resistorelement Rh4, and is formed so that a voltage determined by a seriesresistance value of an internal resistance of the light emitting elementHS1 a and the resistor element Rh3 and the light emission current Ih1 isthe same as a voltage determined by a series resistance value of aninternal resistance of the light emitting element HS2 a and the resistorelement Rh4 and the light emission current Ih2. In this way, the lightemission current Ih1 flowing in the light emitting element group HS1 andthe light emission current Ih2 flowing in the light emitting elementgroup HS2 have the same current value, and hence the light emittingelement group HS1 and the light emitting element group HS2 have the samelight emission luminance. However, if it is not necessary that the lightemitting element group HS1 and the light emitting element group HS2 havethe same light emission luminance, it is not necessary to set theresistance value of the resistor element Rh3 to be larger than theresistance value of the resistor element Rh4.

The light emission control unit HCb includes a comparing circuit CNa, atransistor N1, and a transistor N2.

The comparing circuit CNa includes the resistor element R1, the resistorelement R2, the reference power supply Ref1, and a comparator Cp2. Notethat the connection node between the resistor element R1 and the powersupply circuit VS is Nd1, and hence in this embodiment, the node Nd1 isa connection node between the comparing circuit CNa and the power supplycircuit VS, in other words.

The comparator Cp2 has a noninverting terminal connected to the node Nd2so as to receive the comparison voltage Vc, and an inverting terminalconnected to the other terminal of the reference power supply Ref1 so asto receive the reference voltage Vref1. The comparator Cp2 compares thecomparison voltage Vc with the reference voltage Vref1 and outputs acomparison result signal Vcr2 as a result of the comparison from anoutput terminal. If the comparison voltage Vc is lower than thereference voltage Vref1, the comparator Cp2 outputs the comparisonresult signal Vcr2 of low level that is 0 V, for example. If thecomparison voltage Vc is higher than the reference voltage Vref1, thecomparator Cp2 outputs the comparison result signal Vcr2 of high levelthat is substantially the same as the drive voltage Vk, for example.

As described above, the comparing circuit CNa is connected to the powersupply circuit VS and determines whether the drive voltage Vk is higheror lower than a voltage based on the light emission reference voltageVH, and outputs the comparison result signal Vcr2 as a result.

The transistor N1 is an NMOS transistor and has the gate terminal G as acontrol terminal connected to the output terminal of the comparator Cp2,i.e. to the comparing circuit CNa, the drain terminal D connected to thenode Nh1 a, and the source terminal S connected to the power supply VSS.In other words, the node Nh1 a is connected to the power supply VSS viathe transistor N1. The transistor N1 is on-off controlled by thecomparison result signal Vcr2 that is output from the comparing circuitCNa and is input to the gate terminal G. In this way, light emissioncontrol and light emission stop control of the light emitting elementgroup HS1 are performed.

The transistor N1 is turned off when the low level comparison resultsignal Vcr2 output from the comparing circuit CNa is input to the gateterminal G. In this case, the light emission current Ih1 flowing in thelight emitting element group HS1 is stopped to be 0 A. In other words,supply of the light emission current Ih1 to the light emitting elementgroup HS1 is stopped, and hence the light emitting element group HS1does not emit light. In addition, the transistor N1 is turned on whenthe high level comparison result signal Vcr2 output from the comparatorCp2 is input to the gate terminal G. In this case, because the lightemitting element group HS1 is applied with the light emission voltageVh1 higher than the reference voltage VH1, the light emission currentIh1 flows in the light emitting element group HS1. In this way, thelight emitting element group HS1 emits light.

The transistor N2 is an NMOS transistor and has the gate terminal G as acontrol terminal connected to the output terminal of the comparator Cp2,i.e., to the comparing circuit CNa, the drain terminal D connected tothe node Nh2 a, and the source terminal S connected to the power supplyVSS. In other words, the node Nh2 a is connected to the power supply VSSvia the transistor N2. The transistor N2 is on-off controlled by thecomparison result signal Vcr2 that is output from the comparing circuitCNa and is input to the gate terminal G. In this way, light emissioncontrol and light emission stop control of the light emitting elementgroup HS2 are performed.

When the low level comparison result signal Vcr2 output from thecomparing circuit CNa is input to the gate terminal G, the transistor N2is turned off. In this case, the light emission current Ih2 flowing inthe light emitting element group HS2 is stopped to be 0 A. In otherwords, the supply of the light emission current Ih2 to the lightemitting element group HS2 is stopped, and hence the light emittingelement group HS2 does not emit light. In addition, when the high levelcomparison result signal Vcr2 output from the comparator Cp2 is input tothe gate terminal G, the transistor N2 is turned on. In this case,because the light emission voltage Vh2 higher than the reference voltageVH1 is applied to the light emitting element group HS2, the lightemission current Ih2 flows in the light emitting element group HS2. Inthis way, the light emitting element group HS2 emits light.

As described above, the light emission control unit HCb detects amagnitude relationship between the drive voltage Vk and the lightemission reference voltage VH. If the drive voltage Vk is higher thanthe light emission reference voltage VH, the light emission control unitHCb performs light emission control to cause light emission of the lightemitting element groups HS by turning on the transistor N1 so that thelight emission current Ih1 can be supplied to the light emitting elementgroup HS1, and by turning on the transistor N2 so that the lightemission current Ih2 can be supplied to the light emitting element groupHS2. If the drive voltage Vk is lower than the light emission referencevoltage VH, the light emission control unit HCb performs light emissionstop control to stop light emission of the light emitting element groupsHS by turning off the transistor N1 so that the light emission currentIh1 cannot be supplied to the light emitting element group HS1, and byturning off the transistor N2 so that the light emission current Ih2cannot be supplied to the light emitting element group HS2. Therefore,the lighting device 20 according to this embodiment can cause as well asstop the light emission of the light emitting element group HS1 and thelight emitting element group HS2 at the same time.

Note that the lighting device 20 performs the light emission control andthe light emission stop control by controlling on and off of thetransistor N1 connected between the node Nh1 a and the power supply VSS,and by controlling on and off of the transistor N2 connected between thenode Nh2 a and the power supply VSS, and hence it is not necessary toconnect the PMOS transistors between the power supply circuit VS and thelight emitting element group HS1 as well as the light emitting elementgroup HS2, for performing the light emission control and the lightemission stop control, like the lighting devices 10, 10 a, and 10 b inthe first embodiment. Therefore, the light emission voltage Vh1 based onthe drive voltage Vk output from the power supply circuit VS can besupplied to the light emitting element group HS1 without causing avoltage drop, and the light emission voltage Vh2 can be supplied to thelight emitting element group HS2 without causing a voltage drop.Therefore, the light emitting element group HS1 and the light emittingelement group HS2 can emit light by a lower voltage as the drive voltageVk.

In addition, the lighting device 20 performs the light emission controland the light emission stop control by controlling on and off of thetransistor N1 connected between the node Nh1 a and the power supply VSS,and by controlling on and off of the transistor N2 connected between thenode Nh2 a and the power supply VSS, and hence it is not necessary touse the PMOS transistors for performing the light emission control andthe light emission stop control, like the lighting devices 10, 10 a, and10 b in the first embodiment. In other words, the light emission controland the light emission stop control can be performed by the NMOStransistors that requires a smaller size than the PMOS transistors forachieving the same drive ability, and hence it is possible to reduce thearea of the lighting devices compared with the lighting devices 10, 10a, and 10 b in the first embodiment.

FIGS. 6A to 6E are diagrams illustrating transitions of signal waveformsfrom rising to falling of the power supply to drive the lighting device20. FIG. 6A indicates the transition of the drive voltage Vk in temporalchange. FIG. 6B indicates a relationship between the transition of thecomparison voltage Vc and the reference voltage Vref1 in temporalchange. FIG. 6C indicates the transition of the comparison result signalVcr2 in temporal change. FIG. 6D indicates the transitions of the lightemission voltage Vh1 and the light emission voltage Vh2 in temporalchange. FIG. 6E indicates the transitions of the light emission currentIh1 and the light emission current Ih2 in temporal change. Note that ineach of FIGS. 6A to 6D, the vertical axis represents voltage V, and thehorizontal axis represents time t. Further, in FIG. 6E, the verticalaxis represents current I, and the horizontal axis represents time t.Further, time points t10 to t14 are common among FIGS. 6A to 6E. Inaddition, in FIG. 6E, the light emission current Ih1 and the lightemission current Ih2 are shown to have the same current value, but thisis not a limitation in reality. In addition, in FIGS. 6A to 6E, thesignal waveform described in the first embodiment with reference toFIGS. 2A to 2E is denoted by the same numeral or symbol, and descriptionthereof is appropriately omitted.

At time point t10, drive of the power supply to drive the lightingdevice 20 is started so that the drive voltage Vk starts to increase. Inthis case, the comparison voltage Vc is equal to or lower than 3 V asthe reference voltage Vref1, and hence the comparison result signal Vcr2is low level. In addition, because the comparison result signal Vcr2 islow level, the transistor N1 and the transistor N2 is turned off, thelight emission current Ih1 does not flow in the light emitting elementgroup HS1, and the light emission current Ih2 does not flow in the lightemitting element group HS2. In other words, at time point t10, the lightemitting element groups HS are in off state.

At time point t11, the comparison voltage Vc becomes equal to or higherthan the reference voltage Vref1, and the comparison result signal Vcr2becomes high level so that the transistor N1 and the transistor N2 areturned on. In this case, the light emission voltage Vh1 and the lightemission voltage Vh2 are approximately 9 V, and hence the light emissioncurrent Ih1 flows in the light emitting element group HS1 so that thelight emitting element group HS1 emits light. In addition, the lightemission current Ih2 flows in the light emitting element group HS2 sothat the light emitting element group HS2 emits light. In other words,all the light emitting elements HS1 a of the light emitting elementgroup HS1 and all the light emitting elements HS2 a of the lightemitting element group HS2 emit light at the same timing without avariation.

At time point t12, when the drive of the power supply to drive thelighting device 20 is stopped, the drive voltage Vk starts to decrease.In this case, the comparison voltage Vc, the light emission voltage Vh1,the light emission current Ih1, the light emission voltage Vh2, and thelight emission current Ih2 also start to decrease.

At time point t13, the decreased drive voltage Vk becomes lower than 9V, and the comparison voltage Vc becomes lower than 3 V. In this way,the comparison result signal Vcr2 becomes low level, and hence thetransistor N1 and the transistor N2 are turned off. Then, the lightemission current Ih1 flowing in the light emitting element group HS1 andthe light emission current Ih2 flowing in the light emitting elementgroup HS2 are stopped so that the light emitting element group HS1 andthe light emitting element group HS2 are turned off at the same time. Inthis case, the transistor N1 and the transistor N2 are turned off at atime point when the light emission voltage Vh1 and the light emissionvoltage Vh2 are higher than 8 V as the reference voltage VH2. Therefore,it is avoided that the light emitting element group HS1 and the lightemitting element group HS2 are turned off at different timings with avariation.

At time point t14, the drive voltage Vk is decreased to 0 V. In thisway, drive of the lighting device 20 is stopped.

As described above, in the lighting device 20 according to the secondembodiment of the present invention, the light emission control unit HCbdetects a magnitude relationship between the drive voltage Vk and thelight emission reference voltage VH. If the drive voltage Vk is higherthan the light emission reference voltage VH, the lighting device 20performs light emission control to cause light emission of the lightemitting element groups HS. If the drive voltage Vk is lower than thelight emission reference voltage VH, the lighting device 20 performslight emission stop control to stop light emission of the light emittingelement groups HS. Therefore, it is possible to prevent a variation intiming of causing as well as stopping light emission of the lightemitting element group HS1 and the light emitting element group HS2.

First Variation of Second Embodiment

FIG. 7 is a diagram illustrating a lighting device 20 a according to afirst variation of the second embodiment of the present invention. Thelighting device 20 a includes the power supply circuit VS, the lightemitting element groups HS, the light emission control unit HCb, thedimming circuit LC1, and the dimming circuit LC2. The lighting device 20a according to this variation is substantially different from thelighting device 20 illustrated in FIG. 5 in that the dimming circuit LC1and the dimming circuit LC2 are further provided. Note that in thelighting device 20 a illustrated in FIG. 7, the same structure as in thelighting device 10 a illustrated in FIG. 3, the lighting device 10 billustrated in FIG. 4, or the lighting device 20 illustrated in FIG. 5is denoted by the same numeral or symbol, and description thereof isappropriately omitted.

The dimming circuit LC1 has one terminal connected to the node Nd1 so asto be connected to the power supply circuit VS. In addition, the dimmingcircuit LC1 has the other terminal connected to the node Nh1. In otherwords, the node Nh1 is connected to the power supply circuit VS via thedimming circuit LC1 and the node Nd1. The dimming circuit LC1 adjuststhe light emission current Ih1 flowing in the light emitting elementgroup HS1 to have a predetermined current value.

Note that the lighting device 20 a according to this embodiment has thestructure in which the dimming circuit LC1 is connected between the nodeNd1 and the node Nh1, but this is not a limitation. The dimming circuitLC1 may be connected between the node Nh1 a and the power supply VSS.

The dimming circuit LC2 has one terminal connected to the node Nd1, soas to be connected to the power supply circuit VS. In addition, thedimming circuit LC2 has the other terminal connected to the node Nh2. Inother words, the node Nh2 is connected to the power supply circuit VSvia the dimming circuit LC2 and the node Nd1. In this way, the seriesconnection of the dimming circuit LC2 and the light emitting elementgroup HS2 is connected in parallel to the series connection of thedimming circuit LC1 and the light emitting element group HS1 at the nodeNd1. The dimming circuit LC2 adjusts the light emission current Ih2flowing in the light emitting element group HS2 to have a predeterminedcurrent value.

Note that the lighting device 20 a according to this embodiment has thestructure in which the dimming circuit LC2 is connected between the nodeNd2 and the node Nh2, but this is not a limitation. The dimming circuitLC2 may be connected between the node Nh2 a and the power supply VSS.

Third Embodiment

FIG. 8 is a diagram illustrating a lighting device 30 according to athird embodiment of the present invention. The lighting device 30includes the power supply circuit VS, the light emitting element groupsHS, the dimming circuit LC1, the dimming circuit LC2, and a lightemission control unit HCc. The lighting device 30 according to thisembodiment is substantially different from the lighting device 10 aillustrated in FIG. 3 in that the light emission control unit HCc isprovided instead of the light emission control unit HC, and issubstantially different from the lighting device 10 b illustrated inFIG. 4 in that the light emission control unit HCc is provided insteadof the light emission control unit HCa, and is substantially differentfrom the lighting device 20 a illustrated in FIG. 7 in that the lightemission control unit HCc is provided instead of the light emissioncontrol unit HCb. Note that in the lighting device 30 illustrated inFIG. 8, the same structure as in the lighting device 10 a illustrated inFIG. 3, the lighting device 10 b illustrated in FIG. 4, or the lightingdevice 20 a illustrated in FIG. 7 is denoted by the same numeral orsymbol, and description thereof is appropriately omitted.

The dimming circuit LC1 has one terminal connected to the node Nd1, soas to be connected to the power supply circuit VS. In addition, thedimming circuit LC1 has the other terminal connected to the node Nh1. Inother words, the node Nh1 is connected to the power supply circuit VSvia the dimming circuit LC1 and the node Nd1. The dimming circuit LC1adjusts the light emission current Ih1 flowing in the light emittingelement group HS1 to have a predetermined current value, so as to adjustthe light emission luminance of the light emitting element group HS1.The dimming circuit LC1 includes a transistor P4 as a first dimmingswitch and a comparing circuit CNL1 as a first dimming comparingcircuit.

The comparing circuit CNL1 includes a resistor element R3, a referencepower supply Ref2, and a comparator Cp3.

The resistor element R3 has one terminal connected to the power supplycircuit VS and has a resistance value of 400 ohms, for example.

The reference power supply Ref2 has one terminal connected to the powersupply circuit VS and one terminal of the resistor element R3, andoutputs a reference voltage Vref2 as a first dimming reference voltage.The reference power supply Ref2 outputs the reference voltage Vref2 at apotential that is decreased from the drive voltage Vk by a predeterminedpotential.

The comparator Cp3 has an inverting terminal connected to the otherterminal of the resistor element R3 so as to receive a feedback voltageVfb1 as a first dimming comparison voltage that is a potential of theresistor element R3, and a noninverting terminal connected to the otherterminal of the reference power supply Ref2 so as to receive thereference voltage Vref2. The comparator Cp3 compares the feedbackvoltage Vfb1 with the reference voltage Vref2 and outputs a comparisonresult signal Vcr3 as a first control signal as a result of thecomparison from an output terminal. Here, a connection node between theother terminal of the resistor element R3 and the inverting terminal ofthe comparator Cp3 is referred to as a node Nd4. Note that the voltagelevel of the feedback voltage Vfb1 is determined based on the lightemission voltage Vh1.

The transistor P4 is a PMOS transistor, and its source terminal S isconnected to the node Nd4 that is the other terminal of the resistorelement R3 and is a noninverting terminal of the comparator Cp3, i.e. isconnected to the power supply circuit VS via the resistor element R3,and its drain terminal D is connected to the node Nh1. The transistor P4generates and outputs the light emission voltage Vh1 and the lightemission current Ih1 from the drive voltage Vk supplied to the sourceterminal S from the power supply circuit VS via the resistor element R3.

Here, the comparator Cp3 compares the feedback voltage Vfb1 with thereference voltage Vref2, supplies the comparison result signal Vcr3 tothe gate terminal G of the transistor P4 so that a potential of the nodeNd4 has the same level as the reference voltage Vref2 based on a resultof the comparison, and adjusts the output level of the light emissioncurrent Ih1 output from the transistor P4. If the feedback voltage Vfb1is lower than the reference voltage Vref2, for example, the comparatorCp3 outputs the comparison result signal Vcr3 having a lower voltagelevel so as to increase the potential of the node Nd4, and controls theoutput of the transistor P4 to increase. If the feedback voltage Vfb1 ishigher than the reference voltage Vref2, for example, the comparator Cp3outputs the comparison result signal Vcr3 having a higher voltage levelso as to decrease the potential of the node Nd4, and controls the outputof the transistor P4 to decrease.

As described above, the dimming circuit LC1 adjusts the light emissioncurrent Ih1 output from the transistor P4 to have a predeterminedcurrent value using the comparison result signal Vcr3 output from thecomparing circuit CNL1, and thus adjusts the light emission luminance ofthe light emitting element group HS1.

The dimming circuit LC2 has one terminal connected to the node Nd1, soas to be connected to the power supply circuit VS. In addition, thedimming circuit LC2 has the other terminal connected to the node Nh2. Inother words, the node Nh2 is connected to the power supply circuit VSvia the dimming circuit LC2 and the node Nd1. The dimming circuit LC2adjusts the light emission current Ih2 flowing in the light emittingelement group HS2 to have a predetermined current value, and thusadjusts the light emission luminance of the light emitting element groupHS2. The dimming circuit LC2 includes a transistor P5 as a seconddimming switch, and a comparing circuit CNL2 as a second dimmingcomparing circuit.

The comparing circuit CNL2 includes a resistor element R4, a referencepower supply Ref3, and a comparator Cp4.

The resistor element R4 has one terminal connected to the power supplycircuit VS and has a resistance value of 400 ohms, for example.

The reference power supply Ref3 has one terminal connected to the powersupply circuit VS and one terminal of the resistor element R4 so as tosupply a reference voltage Vref3 as a second dimming reference voltage.In the lighting device 30, the reference voltage Vref3 is supplied as apotential that is decreased from the drive voltage Vk by a predeterminedpotential.

The comparator Cp4 has an inverting terminal connected to the otherterminal of the resistor element R4 so as to receive a feedback voltageVfb2 as a second dimming comparison voltage having a potential of theresistor element R4, and a noninverting terminal connected to the otherterminal of the reference power supply Ref3 so as to receive thereference voltage Vref3. The comparator Cp4 compares the feedbackvoltage Vfb2 with the reference voltage Vref3, and outputs a comparisonresult signal Vcr4 as a second control signal as a result of thecomparison from an output terminal. Here, a connection node between theother terminal of the resistor element R4 and the inverting terminal ofthe comparator Cp4 is referred to as a node Nd5. Note that a voltagelevel of the feedback voltage Vfb2 is determined based on the lightemission voltage Vh2.

The transistor P5 is a PMOS transistor, and its source terminal S isconnected to the node Nd5 that is the other terminal of the resistorelement R4 and is the noninverting terminal of the comparator Cp4, i.e.is connected to the power supply circuit VS via the resistor element R4,and its drain terminal D is connected to the node Nh2. The transistor P5generates and outputs the light emission voltage Vh2 and the lightemission current Ih2 from the drive voltage Vk supplied to the sourceterminal S from the power supply circuit VS via the resistor element R4.

Here, the comparator Cp4 compares the feedback voltage Vfb2 with thereference voltage Vref3, supplies the comparison result signal Vcr4 tothe gate terminal G of the transistor P5 so that a potential of the nodeNd5 has the same level as the reference voltage Vref3 based on a resultof the comparison, and adjusts an output level of the light emissioncurrent Ih2 output from the transistor P5. If the feedback voltage Vfb2is lower than the reference voltage Vref3, for example, the comparatorCp4 outputs the comparison result signal Vcr4 having a lower voltagelevel so as to increase the potential of the node Nd5, and controls theoutput of the transistor P5 to increase. If the feedback voltage Vfb2 ishigher than the reference voltage Vref3, for example, the comparator Cp4outputs the comparison result signal Vcr4 having a higher voltage levelso as to decrease the potential of the node Nd5, and controls the outputof the transistor P5 to decrease.

As described above, the dimming circuit LC2 adjusts the light emissioncurrent Ih2 output from the transistor P5 to have a predeterminedcurrent value using the comparison result signal Vcr4 output from thecomparing circuit CNL2, and thus adjusts the light emission luminance ofthe light emitting element group HS2.

Note that the series connection of the dimming circuit LC1 and the lightemitting element group HS1 is connected in parallel to the seriesconnection of the dimming circuit LC2 and the light emitting elementgroup HS2 with respect to the power supply circuit VS.

The light emission control unit HCc includes a transistor P6, atransistor P7, and the comparing circuit CNa.

The transistor P6 is a PMOS transistor, which has the source terminal Sas one terminal connected to the power supply circuit VS, the drainterminal D as the other terminal connected to the gate terminal G of thetransistor P4, and the gate terminal G as a control terminal connectedto the comparing circuit CNa. The transistor P6 is on-off controlled bythe comparison result signal Vcr2, which is output from the comparingcircuit CNa and is input to the gate terminal G, and thus the lightemission control and the light emission stop control of the lightemitting element group HS1 are performed.

The transistor P6 is turned on when the low level comparison resultsignal Vcr2 is input to the gate terminal G from the comparing circuitCNa. In this way, the transistor P4 becomes off state regardless of theoutput of the comparison result signal Vcr3 because the source terminalS and the gate terminal G are short-circuited. In other words, thetransistor P4 cannot be turned on by the comparison result signal Vcr3so that the supply of the light emission current Ih to the lightemitting element group HS1 is stopped. In other words, the dimmingcircuit LC1 stops generation of the light emission current Ih1 based onthe light emission stop control by the light emission control unit HCc.In the way described above, the light emission stop control of the lightemitting element group HS1 is performed.

The transistor P6 is turned off when the high level comparison resultsignal Vcr2 is input to the gate terminal G from the comparing circuitCNa. In this way, the short-circuit between the source terminal S andthe gate terminal G of the transistor P4 is released so that they areunconnected, and hence a current value of the light emission current Ih1output from the transistor P4 to the light emitting element group HS1can be controlled by the comparison result signal Vcr3. In other words,the dimming circuit LC1 generates the light emission current Ih1 basedon the light emission control by the light emission control unit HCc. Asdescribed above, the light emission control of the light emittingelement group HS1 is performed.

Note that a first threshold voltage for the transistor P6 to be turnedon is preferred to be lower than a second threshold voltage for thetransistor P4 to be turned on. The reason of this is as follows. As tothe transistor P6, if the drive voltage Vk is lower than the lightemission reference voltage VH, the low level comparison result signalVcr2 is input to the gate terminal G while the drive voltage Vk is inputto the source terminal S, and hence the transistor P6 is turned on alongwith an increase of the drive voltage Vk. On the other hand, as to thetransistor P4, the drive voltage Vk is input to the source terminal Swhile the output of the transistor P6 is input to the gate terminal G.In this case, if the second threshold voltage of the transistor P4 islower than the first threshold voltage of the transistor P6, thetransistor P4 is turned on before the transistor P6 is turned on so thatthe gate terminal G and the source terminal S of the transistor P4 areshort-circuited, and hence the light emission voltage Vh1 may be appliedto the light emitting element group HS1 so that the light emittingelement group HS1 may emit light slightly.

The transistor P7 is a PMOS transistor, which has the source terminal Sas one terminal connected to the power supply circuit VS, the drainterminal D as the other terminal connected to the gate terminal G of thetransistor P5, and the gate terminal G as a control terminal connectedto the comparing circuit CNa. The transistor P7 is on-off controlled bythe comparison result signal Vcr2, which is output from the comparingcircuit CNa and is input to the gate terminal G. In this way, the lightemission control and the light emission stop control of the lightemitting element group HS2 are performed.

The transistor P7 is turned on when the low level comparison resultsignal Vcr2 is input to the gate terminal G from the comparing circuitCNa. In this way, the transistor P5 becomes off state regardless of theoutput of the comparison result signal Vcr4 because the source terminalS and the gate terminal G are short-circuited. In other words, thetransistor P5 cannot be turned on by the comparison result signal Vcr4so that the supply of the light emission current Ih2 to the lightemitting element group HS2 is stopped. In other words, the dimmingcircuit LC2 stops generation of the light emission current Ih2 based onthe light emission stop control by the light emission control unit HCc.In the way described above, the light emission stop control of the lightemitting element group HS2 is performed.

The transistor P7 is turned off when the high level comparison resultsignal Vcr2 is input to the gate terminal G from the comparing circuitCNa. In this way, the short-circuit between the source terminal S andthe gate terminal G of the transistor P5 is released so that they areunconnected, and hence a current value of the light emission current Ih2output from the transistor P5 to the light emitting element group HS2can be controlled by the comparison result signal Vcr4. In other words,the dimming circuit LC2 generates the light emission current Ih2 basedon the light emission control by the light emission control unit HCc. Asdescribed above, the light emission control of the light emittingelement group HS2 is performed.

Note that a third threshold voltage for the transistor P7 to be turnedon is preferred to be lower than a fourth threshold voltage for thetransistor P5 to be turned on. The reason of this is as follows. As tothe transistor P7, if the drive voltage Vk is lower than the lightemission reference voltage VH, the low level comparison result signalVcr2 is input to the gate terminal G while the drive voltage Vk is inputto the source terminal S, and hence the transistor P7 is turned on alongwith an increase of the drive voltage Vk. On the other hand, as to thetransistor P5, the drive voltage Vk is input to the source terminal Swhile the output of the transistor P7 is input to the gate terminal G.In this case, if the fourth threshold voltage of the transistor P5 islower than the third threshold voltage of the transistor P7, thetransistor P5 is turned on before the transistor P7 is turned on so thatthe gate terminal G and the source terminal S of the transistor P5 areshort-circuited, and hence the light emission voltage Vh2 may be appliedto the light emitting element group HS1 so that the light emittingelement group HS2 may emit light slightly.

As described above, the light emission control unit HCc detects amagnitude relationship between the drive voltage Vk and the lightemission reference voltage VH. If the drive voltage Vk is higher thanthe light emission reference voltage VH, the light emission control unitHCc performs the light emission control to cause light emission of thelight emitting element groups HS by turning off the transistor P6 toenable control of the output of the transistor P4 by the comparisonresult signal Vcr3, and by turning off the transistor P7 to enablecontrol of the output of the transistor P5 by the comparison resultsignal Vcr4, so that the light emission current Ih1 can be supplied tothe light emitting element group HS1 and that the light emission currentIh2 can be supplied light emitting element group HS2. In other words,the light emission control unit HCc performs light emission control sothat the dimming circuit LC1 can generate the light emission current Ih1while the dimming circuit LC2 can generate the light emission currentIh2. In addition, if the drive voltage Vk is lower than the lightemission reference voltage VH, the light emission control unit HCcperforms the light emission stop control to stop light emission of thelight emitting element groups HS by turning on the transistor P6 and thetransistor P7 so that the outputs of the transistor P4 and thetransistor P5 of the dimming circuit LC1 cannot be controlled by thecomparison result signal Vcr3 and are forcibly stopped, so that thelight emission current Ih1 cannot be supplied to the light emittingelement group HS1, and that the light emission current Ih2 cannot besupplied to the light emitting element group HS2. In other words, thelight emission control unit HCc performs the light emission stop controlso that the dimming circuit LC1 cannot generate the light emissioncurrent Ih1, and that the dimming circuit LC2 cannot generate the lightemission current Ih2. Therefore, the lighting device 30 according tothis embodiment can cause as well as stop the light emission of thelight emitting element group HS1 and the light emitting element groupHS2 at the same time.

FIGS. 9A to 9E are diagram illustrating transitions of signal waveformsfrom rising to falling of a power supply to drive the lighting device30. FIG. 9A indicates the transition of the drive voltage Vk in temporalchange. FIG. 9B indicates a relationship between the transition of thecomparison voltage Vc and the reference voltage Vref1 in temporalchange. FIG. 9C indicates the transition of the comparison result signalVcr2 in temporal change. FIG. 9D indicates the transitions of the lightemission voltage Vh1 and the light emission voltage Vh2 in temporalchange. FIG. 9E indicates the transition of the light emission currentIh1 and the light emission current Ih2 in temporal change. Note that, ineach of FIGS. 9A to 9D, the vertical axis represents voltage V, and thehorizontal axis represents time t. Further, in FIG. 9E, the verticalaxis represents current I, and the horizontal axis represents time t.Further, time points t20 to t24 are common among FIGS. 9A to 9E. Inaddition, in FIG. 9E, the light emission current Ih1 and the lightemission current Ih2 are shown to have the same current value, but thisis not a limitation in reality. In addition, in FIGS. 9A to 9E, thesignal waveform described in second embodiment with reference to FIGS.6A to 6E is denoted by the same numeral or symbol, and descriptionthereof is appropriately omitted.

At time point t20, the drive of the power supply to drive the lightingdevice 30 is started so that the drive voltage Vk starts to increase. Inthis case, because the comparison voltage Vc is equal to or lower than 3V as the reference voltage Vref1, the comparison result signal Vcr2 haslow level. In addition, because the comparison result signal Vcr2 haslow level, the drive voltage Vk increases. When the gate-source voltageof the transistor P6 exceeds a threshold value, the transistor P6 isturned on. When the gate-source voltage of the transistor P7 exceeds athreshold value, the transistor P7 is turned on. In this way, the gateterminal G and the source terminal S of the transistor P4 areshort-circuited so that the transistor P4 is turned off. In addition,the gate terminal G and the source terminal S of the transistor P5 areshort-circuited so that the transistor P5 is turned off. Therefore, thelight emission voltage Vh1 is 0 V so that the light emission current Ih1does not flow in the light emitting element group HS1, and the lightemission voltage Vh2 is 0 V so that the light emission current Ih2 doesnot flow in the light emitting element group HS2. In other words, thelight emitting element group HS1 and the light emitting element groupHS2 are both turned off.

At time point t21, the comparison voltage Vc becomes equal to or higherthan the reference voltage Vref1, and the comparison result signal Vcr2is changed to high level, so that the transistor P6 and the transistorP7 are turned off. In this way, the short-circuit between the gateterminal G and the source terminal S of the transistor P4 is released sothat the output of the transistor P4 can be adjusted by the comparisonresult signal Vcr3, and hence the light emission luminance of the lightemitting element group HS1 can be adjusted. Here, because the lightemission voltage Vh1 is approximately 9 V, when the transistor P4 isturned on, the light emission current Ih1 flows in the light emittingelement group HS1 so that the light emitting element group HS1 emitslight. In addition, the short-circuit between the gate terminal G andthe source terminal S of the transistor P5 is released, and hence theoutput of the transistor P5 can be adjusted by the comparison resultsignal Vcr4. Thus, the light emission luminance of the light emittingelement group HS2 can be adjusted. Here, because the light emissionvoltage Vh2 is approximately 9 V, when the transistor P5 is turned on,the light emission current Ih2 flows in the light emitting element groupHS2 so that the light emitting element group HS2 emits light. In otherwords, all the light emitting elements HS1 a of the light emittingelement group HS1 and all the light emitting elements HS2 a of the lightemitting element group HS2 emit light at the same timing without avariation.

At time point t22, the drive of the power supply to drive the lightingdevice 30 is stopped, and then the drive voltage Vk starts to decrease.In this case, the comparison voltage Vc, the light emission voltage Vh1,the light emission current Ih1, the light emission voltage Vh2, and thelight emission current Ih2 also start to decrease.

At time point t23, the decreasing drive voltage Vk becomes lower than 9V, and the comparison voltage Vc becomes lower than 3 V. In this way,the comparison result signal Vcr2 is changed to low level, and again thetransistor P6 and the transistor P7 are turned on while the transistorP4 and the transistor P5 are turned off. Then, the light emissioncurrent Ih1 flowing in the light emitting element group HS1 and thelight emission current Ih2 flowing in the light emitting element groupHS2 are stopped so that the light emitting element group HS1 and thelight emitting element group HS2 are turned off at the same time. Inthis case, the transistor P4 and the transistor P5 are turned off at atime point when the light emission voltage Vh1 and the light emissionvoltage Vh2 are higher than 8 V as the reference voltage VH2, and henceit is avoided that the light emitting element group HS1 and the lightemitting element group HS2 are turned off at different timings with avariation.

At time point t24, the drive voltage Vk is decreased to 0 V. In thisway, the drive of the lighting device 30 is stopped.

As described above, in the lighting device 30 according to the thirdembodiment of the present invention, the light emission control unit HCcdetects a magnitude relationship between the drive voltage Vk and thelight emission reference voltage VH, performs light emission control tocause light emission of the light emitting element groups HS if thedrive voltage Vk is higher than the light emission reference voltage VH,and performs light emission stop control to stop light emission of thelight emitting element groups HS if the drive voltage Vk is lower thanthe light emission reference voltage VH. Therefore, it is possible toprevent a variation in timing of causing as well as stopping lightemission of the light emitting element group HS1 and the light emittingelement group HS2.

In addition, in the lighting device 30 according to the third embodimentof the present invention, the dimming circuit LC1 stops generation ofthe light emission current Ih1 based on the light emission stop controlby the light emission control unit HCc, and generates the light emissioncurrent Ih1 based on the light emission control by the light emissioncontrol unit HCc. In addition, the dimming circuit LC2 stops generationof the light emission current Ih2 based on the light emission stopcontrol by the light emission control unit HCc, and generates the lightemission current Ih2 based on the light emission control by the lightemission control unit HCc. Therefore, it is not necessary to dispose atransistor for performing the light emission control or the lightemission stop control in the path of current for causing light emissionof the light emitting element groups HS like the lighting devices 10, 10a, 10 b, 20, and 20 a. Therefore, it is possible to suppress an increasein a circuit area of the lighting device that may occur when using thepresent invention.

Note that the lighting device 30 according to this embodiment has thestructure in which the dimming circuit LC1 is connected between thepower supply circuit VS and the node Nh1, and the dimming circuit LC2 isconnected between the power supply circuit VS and the node Nh2 asdescribed above, but this is not a limitation. It is possible to adopt astructure in which the dimming circuit LC1 is connected between the nodeNh1 a and the power supply VSS, and the dimming circuit LC2 is connectedbetween the node Nh2 a and the power supply VSS. In this case too, whenadopting the structure in which the dimming circuit LC1 generates thelight emission current Ih1 based on the light emission control and stopsgeneration of the light emission current Ih1 based on the light emissionstop control, and the dimming circuit LC2 generates the light emissioncurrent Ih2 based on the light emission control and stops generation ofthe light emission current Ih2 based on the light emission stop control,it is possible to achieve the effect obtained by this embodiment, i.e.,to suppress an increase in the circuit area.

In addition, in the lighting device 30 according to this embodiment, thenoninverting terminal of the comparator Cp4 is connected to the otherterminal of the reference power supply Ref3 so that the referencevoltage Vref3 is supplied, as an example, but this is not a limitation.It is possible to supply the reference voltage Vref3 to the noninvertingterminal of the comparator Cp4 from the reference power supply Ref2. Inthis case, it is preferred to adopt the structure in which, instead ofthe reference power supply Ref3, the other terminal of the referencepower supply Ref2, whose one terminal is connected to the power supplycircuit VS and one terminal of the resistor element R3, is connected tothe noninverting terminal of the comparator Cp3 and is connected to thenoninverting terminal of the comparator Cp4. In this way, it is possibleto suppress an increase in the area of the lighting device 30.

First Variation of Third Embodiment

FIG. 10 is a diagram illustrating a lighting device 30 a according to afirst variation of the third embodiment of the present invention. Thelighting device 30 a includes the power supply circuit VS, the lightemitting element groups HS, the dimming circuit LC1, the dimming circuitLC2, and the light emission control unit HCc. In the lighting device 30a according to this variation, the connection destinations of thetransistor P6 and the transistor P7 of the light emission control unitHCc are substantially different from those in the lighting device 30illustrated in FIG. 8. Note that in the lighting device 30 a illustratedin FIG. 10, the same structure as in the lighting device 30 illustratedin FIG. 8 is denoted by the same numeral or symbol, and descriptionthereof is appropriately omitted.

The transistor P6 has the drain terminal D as the other terminalconnected to the other terminal of the reference power supply Ref2 andthe noninverting terminal of the comparator Cp3.

The transistor P6 is turned on when the low level comparison resultsignal Vcr1 is input to the gate terminal G from the comparing circuitCNa. In this way, the noninverting terminal of the comparator Cp3 issupplied with the drive voltage Vk as the reference voltage Vref2regardless of the potential supplied by the reference power supply Ref2,and the comparison result signal Vcr3 output from the comparator Cp3 issupplied to the gate terminal G of the transistor P4, so that thefeedback voltage Vfb1 has the same level as the reference voltage Vref2,i.e. so that the drive voltage Vk does not cause a voltage drop by theresistor element R3, in other words, so that potentials on both ends ofthe resistor element R3 have the same level, and the transistor P4 isturned off so that the supply of the light emission current Ih1 to thelight emitting element group HS1 is stopped. In other words, the dimmingcircuit LC1 stops generation of the light emission current Ih1 based onthe light emission stop control by the light emission control unit HCc.In the way described above, the light emission stop control of the lightemitting element group HS1 is performed.

In addition, the transistor P6 is turned off when the high levelcomparison result signal Vcr1 is input to the gate terminal G from thecomparing circuit CNa. In this way, because a voltage supplied from thereference power supply Ref2 is supplied as the reference voltage Vref2to the noninverting terminal of the comparator Cp3, a current value ofthe light emission current Ih1 output from the transistor P4 to thelight emitting element group HS1 can be controlled by the comparisonresult signal Vcr3. In other words, the dimming circuit LC1 generatesthe light emission current Ih1 based on the light emission control bythe light emission control unit HCc. As described above, the lightemission control of the light emitting element group HS1 is performed.

The transistor P7 has the drain terminal D as the other terminalconnected to the other terminal of the reference power supply Ref3 andthe noninverting terminal of the comparator Cp4.

The transistor P7 is turned on when the low level comparison resultsignal Vcr1 is input to the gate terminal G from the comparing circuitCNa. In this way, the noninverting terminal of the comparator Cp4 issupplied with the drive voltage Vk as the reference voltage Vref3regardless of the potential supplied by the reference power supply Ref3,and the comparison result signal Vcr4 output from the comparator Cp4 issupplied to the gate terminal G of the transistor P5, so that thefeedback voltage Vfb2 has the same level as the reference voltage Vref3,i.e. so that the drive voltage Vk does not cause a voltage drop by theresistor element R4, in other words, so that potentials on both ends ofthe resistor element R4 have the same level, and the transistor P5 isturned off so that the supply of the light emission current Ih2 to thelight emitting element group HS2 is stopped. In other words, the dimmingcircuit LC2 stops generation of the light emission current Ih2 based onthe light emission stop control by the light emission control unit HCc.In the way described above, the light emission stop control of the lightemitting element group HS2 is performed.

In addition, the transistor P7 is turned off when the high levelcomparison result signal Vcr1 is input to the gate terminal G from thecomparing circuit CNa. In this way, because a voltage supplied from thereference power supply Ref3 is supplied as the reference voltage Vref3to the noninverting terminal of the comparator Cp4, a current value ofthe light emission current Ih2 output from the transistor P5 to thelight emitting element group HS2 can be controlled by the comparisonresult signal Vcr4. In other words, the dimming circuit LC2 generatesthe light emission current Ih2 based on the light emission control bythe light emission control unit HCc. As described above, the lightemission control of the light emitting element group HS2 is performed.

As described above, the light emission control unit HCc detects amagnitude relationship between the drive voltage Vk and the lightemission reference voltage VH. If the drive voltage Vk is higher thanthe light emission reference voltage VH, the light emission control unitHCc performs the light emission control to cause light emission of thelight emitting element groups HS by turning off the transistor P6 toenable control of the output of the transistor P4 by the comparisonresult signal Vcr3, and by turning off the transistor P7 to enablecontrol of the output of the transistor P5 by the comparison resultsignal Vcr4, so that the light emission current Ih1 can be supplied tothe light emitting element group HS1 and that the light emission currentIh2 can be supplied to the light emitting element group HS2. In otherwords, the light emission control unit HCc performs light emissioncontrol so that the dimming circuit LC1 can generate the light emissioncurrent Ih1 while the dimming circuit LC2 can generate the lightemission current Ih2. In addition, if the drive voltage Vk is lower thanthe light emission reference voltage VH, the light emission control unitHCc performs the light emission stop control to stop light emission ofthe light emitting element groups HS by turning on the transistor P6 andthe transistor P7 to forcibly stop the outputs of the transistor P4 andthe transistor P5 of the dimming circuit LC1, so that the light emissioncurrent Ih1 cannot be supplied to the light emitting element group HS1,and that the light emission current Ih2 cannot be supplied to the lightemitting element group HS2. In other words, the light emission controlunit HCc performs the light emission stop control so that the dimmingcircuit LC1 cannot generate the light emission current Ih1, and that thedimming circuit LC2 cannot generate the light emission current Ih2.Therefore, the lighting device 30 according to this embodiment can causeas well as stop the light emission of the light emitting element groupHS1 and the light emitting element group HS2 at the same time.

In addition, the lighting device 30 a according to this embodimentperforms the light emission control and the light emission stop controlby the comparing circuit CNa and the two transistors, i.e. thetransistor P6 and the transistor P7 of the light emission control unitHCc, but this is not a limitation. It is possible to perform the controlby the comparing circuit CNa and the transistor P6. In this case, it ispreferred to adopt a structure in which the drain terminal D of thetransistor P6, instead of the transistor P7, is connected to thenoninverting terminal of the comparator Cp3 and is also connected to thenoninverting terminal of the comparator Cp4.

Second Variation of Third Embodiment

FIG. 11 is a diagram illustrating a lighting device 30 b according to asecond variation of the third embodiment of the present invention. Thelighting device 30 b includes the power supply circuit VS, the lightemitting element groups HS, the dimming circuit LC1, the dimming circuitLC2, and a light emission control unit HCd. The lighting device 30 baccording to this variation is substantially different from the lightingdevice 30 illustrated in FIG. 8 in that the light emission control unitHCd is provided instead of the light emission control unit HCc. Notethat in the lighting device 30 b illustrated in FIG. 11, the samestructure as in the lighting device 30 illustrated in FIG. 8 is denotedby the same numeral or symbol, and description thereof is appropriatelyomitted.

The comparator Cp3 of the dimming circuit LC1 is connected to the powersupply circuit VS and receives supply of the drive voltage Vk outputfrom the power supply circuit VS so as to be driven. In other words, thecomparison result signal Vcr3 is generated based on the drive voltageVk.

The comparator Cp4 of the dimming circuit LC2 is connected to the powersupply circuit VS and receives supply of the drive voltage Vk outputfrom the power supply circuit VS so as to be driven. In other words, thecomparison result signal Vcr4 is generated based on the drive voltageVk.

The light emission control unit HCd includes a transistor N3, atransistor N4, and the comparing circuit CNa.

The transistor N3 is an NMOS transistor, which has the source terminal Sas one terminal connected to the power supply VSS and the drain terminalD as the other terminal connected to the comparator Cp3. In this way,the comparator Cp3 is connected to the power supply VSS via thetransistor N3. In addition, the transistor N3 has the gate terminal G asa control terminal connected to the comparing circuit CNa. Thetransistor N3 is on-off controlled by the comparison result signal Vcr2,which is output from the comparing circuit CNa and is input to the gateterminal G. In this way, the light emission control and the lightemission stop control of the light emitting element group HS1 areperformed.

The transistor N3 is turned off when the low level comparison resultsignal Vcr2 is input to the gate terminal G from the comparing circuitCNa. In this way, the connection between the comparator Cp3 and thepower supply VSS is interrupted, the comparison result signal Vcr3output from the comparator Cp3 is forcibly set to high level, and thegate terminal G of the transistor P4 is supplied with a voltage havingsubstantially the same level as the drive voltage Vk. In this way, thetransistor P4 is forcibly turned off regardless of a result of thecomparison between the reference voltage Vref2 and the feedback voltageVfb1 by the comparator Cp3, and hence the supply of the light emissioncurrent Ih1 to the light emitting element group HS1 is stopped. In otherwords, the dimming circuit LC1 stops generation of the light emissioncurrent Ih1 based on the light emission stop control by the lightemission control unit HCd. In the way described above, the lightemission stop control of the light emitting element group HS1 isperformed.

In addition, the transistor N3 is turned on when the high levelcomparison result signal Vcr2 is input to the gate terminal G from thecomparing circuit CNa. In this way, the comparator Cp3 and the powersupply VSS are electrically connected to each other, and the comparatorCp3 can output the comparison result signal Vcr3 based on a result ofthe comparison between the reference voltage Vref2 and the feedbackvoltage Vfb1. Therefore, the current value of the light emission currentIh1 output from the transistor P4 to the light emitting element groupHS1 can be controlled by the comparison result signal Vcr3. In otherwords, the dimming circuit LC1 generates the light emission current Ih1based on the light emission control by the light emission control unitHCd. As described above, the light emission control of the lightemitting element group HS1 is performed.

The transistor N4 is an NMOS transistor, which has the source terminal Sas one terminal connected to the power supply VSS, and the drainterminal D as the other terminal connected to the comparator Cp4. Inthis way, the comparator Cp4 is connected to the power supply VSS viathe transistor N4. In addition, the transistor N4 has the gate terminalG as a control terminal connected to the comparing circuit CNa. Thetransistor N4 is on-off controlled by the comparison result signal Vcr2,which is output from the comparing circuit CNa and is input to the gateterminal G, and thus the light emission control and the light emissionstop control of the light emitting element group HS2 are performed.

The transistor N4 is turned off when the low level comparison resultsignal Vcr2 is input to the gate terminal G of the comparing circuitCNa. In this way, the connection between the comparator Cp4 and thepower supply VSS is interrupted, the comparison result signal Vcr4output from the comparator Cp4 is forcibly set to high level, and thegate terminal G of the transistor P5 is supplied with a voltage havingsubstantially the same level as the drive voltage Vk. In this way, thetransistor P5 is forcibly turned off regardless of a result of thecomparison between the reference voltage Vref3 and the feedback voltageVfb1 by the comparator Cp3, and hence the supply of the light emissioncurrent Ih2 to the light emitting element group HS2 is stopped. In otherwords, the dimming circuit LC2 stops generation of the light emissioncurrent Ih2 based on the light emission stop control by the lightemission control unit HCd. In the way described above, the lightemission stop control of the light emitting element group HS2 isperformed.

In addition, the transistor N4 is turned on when the high levelcomparison result signal Vcr2 is input to the gate terminal G from thecomparing circuit CNa. In this way, the comparator Cp4 and the powersupply VSS are electrically connected to each other, and hence thecomparator Cp4 can output the comparison result signal Vcr4 based on aresult of the comparison between the reference voltage Vref3 and thefeedback voltage Vfb2. Therefore, the current value of the lightemission current Ih2 output from the transistor P5 to the light emittingelement group HS2 can be controlled by the comparison result signalVcr4. In other words, the dimming circuit LC2 generates the lightemission current Ih2 based on the light emission control by the lightemission control unit HCd. In the way described above, the lightemission control of the light emitting element group HS2 is performed.

As described above, the light emission control unit HCd detects amagnitude relationship between the drive voltage Vk and the lightemission reference voltage VH. If the drive voltage Vk is higher thanthe light emission reference voltage VH, the light emission control unitHCd performs the light emission control to cause light emission of theof the light emitting element groups HS by turning on the transistor N3to enable control of the output of the transistor P4 by the comparisonresult signal Vcr3 based on the comparison between the reference voltageVref2 and the feedback voltage Vfb1, and by turning on the transistor N4to enable control of the output of the transistor P5 by the comparisonresult signal Vcr4 based on the comparison between the reference voltageVref3 and the feedback voltage Vfb2, so that the light emission currentIh1 can be supplied to the light emitting element group HS1 and that thelight emission current Ih2 can be supplied to the light emitting elementgroup HS2. In other words, the light emission control unit HCd performsthe light emission control so that the dimming circuit LC1 can generatethe light emission current Ih1 while the dimming circuit LC2 cangenerate the light emission current Ih2. In addition, if the drivevoltage Vk is lower than the light emission reference voltage VH, thelight emission control unit HCd performs the light emission stop controlto stop light emission of the light emitting element groups HS byturning off the transistor N3 to disable control of the output of thetransistor P4 of the dimming circuit LC1 to be forcibly turned off bythe comparison result signal Vcr3 based on the comparison between thereference voltage Vref2 and the feedback voltage Vfb1, and by turningoff the transistor N4 to disable control of the output of the transistorP5 of the dimming circuit LC2 to be forcibly turned off by thecomparison result signal Vcr4 based on the comparison between thereference voltage Vref3 and the feedback voltage Vfb2, so that the lightemission current Ih1 cannot be supplied to the light emitting elementgroup HS1, and that the light emission current Ih2 cannot be supplied tothe light emitting element group HS2. In other words, the light emissioncontrol unit HCd performs the light emission stop control so that thedimming circuit LC1 cannot generate the light emission current Ih1, andthat the dimming circuit LC2 cannot generate the light emission currentIh2. Therefore, the lighting device 30 according to this embodiment cancause as well as stop the light emission of the light emitting elementgroup HS1 and the light emitting element group HS2 at the same time.

In addition, the lighting device 30 b according to this embodimentperforms the light emission control and the light emission stop controlby the comparing circuit CNa and the two transistors, i.e. thetransistor N3 and the transistor N4 of the light emission control unitHCd, but this is not a limitation. It is possible to perform the controlby the comparing circuit CNa and the transistor N3. In this case, it ispreferred to adopt a structure in which the drain terminal D of thetransistor N3 is connected to the comparator Cp3 and is also connectedto the comparator Cp4.

Third Variation of Third Embodiment

FIG. 12 is a diagram illustrating a lighting device 30 c according to athird variation of the third embodiment of the present invention. Thelighting device 30 c includes the power supply circuit VS, the lightemitting element groups HS, the light emission control unit HCe, adimming circuit LC11, and a dimming circuit LC12. The lighting device 30c according to this variation is substantially different from thelighting device 30 illustrated in FIG. 8 in that the light emissioncontrol unit HCe is provided instead of the light emission control unitHCc, and that the dimming circuit LC11 and the dimming circuit LC12 areprovided instead of the dimming circuit LC1 and the dimming circuit LC2.Note that in the lighting device 30 c illustrated in FIG. 12, the samestructure as in the lighting device 30 illustrated in FIG. 8 is denotedby the same numeral or symbol, and description thereof is appropriatelyomitted.

The light emission control unit HCe detects a magnitude relationshipbetween the drive voltage Vk and the light emission reference voltageVH, performs light emission control to cause light emission of the lightemitting element groups HS if the drive voltage Vk is higher than thelight emission reference voltage VH, and performs light emission stopcontrol to stop light emission of the light emitting element groups HSif the drive voltage Vk is lower than the light emission referencevoltage VH. The light emission control unit HCe includes the comparingcircuit CN.

The dimming circuit LC11 has one terminal connected to the node Nd1, andthus is connected to the power supply circuit VS. In addition, thedimming circuit LC11 has the other terminal connected to the node Nh1.In other words, the node Nh1 is connected to the power supply circuit VSvia the dimming circuit LC11 and the node Nd1. The dimming circuit LC11adjusts the light emission current Ih1 flowing in the light emittingelement group HS1 to have a predetermined current value, and henceadjusts the light emission luminance of the light emitting element groupHS1. The dimming circuit LC11 includes a transistor PD1 as the firstdimming switch, a current generator circuit VC1 as a first currentgenerator circuit, a comparing circuit CNL11 as the first dimmingcomparing circuit, and a driving circuit KD1 as a first driving circuit.

The transistor PD1 is a PMOS transistor having the source terminal Sconnected to the power supply circuit VS.

The current generator circuit VC1 includes an inductor L1, a capacitorC1, and a rectifier diode D1. The inductor L1 has one terminal connectedto the drain terminal D of the transistor PD1. The capacitor C1 has oneterminal connected to the other terminal of the inductor L1 and theother terminal connected to the power supply VSS. The rectifier diode D1has the anode connected to the power supply VSS and the cathodeconnected to a connection node between the drain terminal D of thetransistor PD1 and one terminal of the inductor L1.

When the transistor PD1 is on, in the current generator circuit VC1, theinductor L1 stores magnetic energy based on the drive voltage Vk outputfrom the transistor PD1, and the capacitor C1 smooths the same so as togenerate and output the light emission voltage Vh1 and the lightemission current Ih1. In addition, when the transistor PD1 is off, inthe current generator circuit VC1, the magnetic energy stored in theinductor L1 is supplied to the capacitor C1 via the rectifier diode D1,the capacitor C1 smooths the magnetic energy so as to generate andoutput the light emission voltage Vh1 and the light emission currentIh1. In other words, the current generator circuit VC1 steps down thedrive voltage Vk obtained by turning on and off the transistor PD1, soas to generate and output the light emission voltage Vh1 and the lightemission current Ih1.

The comparing circuit CNL11 includes a reference power supply Ref4 and acomparator Cp5.

The reference power supply Ref4 has one terminal connected to the powersupply VSS and generates a reference voltage Vref4 as the first dimmingreference voltage. The reference voltage Vref4 is e.g. 2 V.

The comparator Cp5 has the noninverting terminal connected to a node Nd8as a connection node between the node Nh1 a and the resistor element Rh1so as to receive a feedback voltage Vfb3 as the first dimming comparisonvoltage that is a potential at the node Nd8, and the inverting terminalconnected to the reference power supply Ref4 so as to receive thereference voltage Vref4. The comparator Cp5 compares the feedbackvoltage Vfb3 with the reference voltage Vref4, outputs the comparisonresult signal Vcr5 as the first control signal so that the potential atthe node Nd8 becomes the same level as the reference voltage Vref4 basedon a result of the comparison, and adjusts the light emission currentIh1 generated by the transistor PD1 and the current generator circuitVC1. If the feedback voltage Vfb3 is lower than the reference voltageVref4, for example, the comparator Cp5 outputs the high level comparisonresult signal Vcr5 so as to increase the potential at the node Nd8. Inaddition, if the feedback voltage Vfb3 is higher than the referencevoltage Vref4, the comparator Cp5 outputs the low level comparisonresult signal Vcr5 so as to decrease the potential at the node Nd8.

In the way described above, the comparing circuit CNL11 detects thefeedback voltage Vfb3 based on the light emission voltage Vh1, outputsthe comparison result signal Vcr5 so that the light emission current Ih1flowing in the light emitting element group HS1 becomes a desired value,and adjusts the output of the transistor PD1.

The driving circuit KD1 is connected to the gate terminal G as a controlterminal of the transistor PD1 and the output terminal of the comparatorCp5 in the comparing circuit CNL11, and supplies the drive signal Vs1 asa first drive signal to the transistor PD1 in accordance with thecomparison result signal Vcr5 output from the comparator Cp5, i.e. thecomparing circuit CNL11. When receiving the low level comparison resultsignal Vcr5, for example, the driving circuit KD1 supplies the highlevel drive signal Vs1 at for example 5 V to the gate terminal G of thetransistor PD1. In this way, the transistor PD1 is turned off, and thesupply of a voltage based on the drive voltage Vk to the inductor L1 isstopped. In addition, when receiving the high level comparison resultsignal Vcr5, for example, the driving circuit KD1 supplies the low leveldrive signal Vs' at 0 V for example to the gate terminal G of thetransistor PD1. In this way, the transistor PD1 is turned on, and thevoltage based on the drive voltage Vk is supplied to the inductor L1.Note that the driving circuit KD1 may have a structure for performing aPWM control in which a PWM signal having a predetermined duty ratio issupplied to the gate terminal G of the transistor PD1.

As described above, the dimming circuit LC11 adjusts the light emissioncurrent Ih1 output from the transistor PD1 to have a predeterminedcurrent value by the drive signal Vs1 based on the comparison resultsignal Vcr5 output from the comparing circuit CNL11, and thus adjuststhe light emission luminance of the light emitting element group HS1.

The dimming circuit LC12 has one terminal connected to the node Nd1, andhence is connected to the power supply circuit VS. In addition, thedimming circuit LC12 has the other terminal connected to the node Nh2.In other words, the node Nh2 is connected to the power supply circuit VSvia the dimming circuit LC12 and the node Nd1. The dimming circuit LC12adjusts the light emission current Ih2 flowing in the light emittingelement group HS2 to have a predetermined current value, and thusadjusts the light emission luminance of the light emitting element groupHS2. The dimming circuit LC12 includes a transistor PD2 as the seconddimming switch, a current generator circuit VC2 as a second currentgenerator circuit, a comparing circuit CNL12 as the second dimmingcomparing circuit, and a driving circuit KD2 as a second drivingcircuit.

The transistor PD2 is a PMOS transistor having the source terminal Sconnected to the power supply circuit VS.

The current generator circuit VC2 includes an inductor L2, a capacitorC2, and a rectifier diode D2. The inductor L2 has one terminal connectedto the drain terminal D of the transistor PD2. The capacitor C2 has oneterminal connected to the other terminal of the inductor L2 and theother terminal connected to the power supply VSS. The rectifier diode D2has the anode connected to the power supply VSS and the cathodeconnected to a connection node between the drain terminal D of thetransistor PD2 and one terminal of the inductor L2.

When the transistor PD2 is on, in the current generator circuit VC2, theinductor L2 stores magnetic energy based on the drive voltage Vk outputfrom the transistor PD2, and the capacitor C2 smooths the same so as togenerate and output the light emission voltage Vh2 and the lightemission current Ih2. In addition, when the transistor PD2 is off, inthe current generator circuit VC2, the magnetic energy stored in theinductor L2 is supplied to the capacitor C2 via the rectifier diode D2,and the capacitor C2 smooths the magnetic energy so as to generate andoutput the light emission voltage Vh2 and the light emission currentIh2. In other words, the current generator circuit VC2 steps down thedrive voltage Vk obtained by turning on and off the transistor PD2, soas to generate and output the light emission voltage Vh2 and the lightemission current Ih2.

The comparing circuit CNL12 includes a reference power supply Ref5 and acomparator Cp6.

The reference power supply Ref5 has one terminal connected to the powersupply VSS so as to generate a reference voltage Vref5 as the seconddimming reference voltage. The reference voltage Vref5 is e.g. 2 V.

The comparator Cp6 has the noninverting terminal connected to a node Nd9that is a connection node between the node Nh2 a and the resistorelement Rh2 so as to receive a feedback voltage Vfb4 as the seconddimming comparison voltage that is a potential at the node Nd9, and theinverting terminal connected to the reference power supply Ref5 so as toreceive the reference voltage Vref5. The comparator Cp6 compares thefeedback voltage Vfb4 with the reference voltage Vref5, outputs acomparison result signal Vcr6 as the second control signal so that thepotential at the node Nd9 becomes the same level as the referencevoltage Vref5 based on a result of the comparison, and adjusts the lightemission current Ih2 generated by the transistor PD2 and the currentgenerator circuit VC2. If the feedback voltage Vfb4 is lower than thereference voltage Vref5, for example, the comparator Cp6 outputs thehigh level comparison result signal Vcr6 so as to increase a potentialof the node Nd9. In addition, if the feedback voltage Vfb4 is higherthan the reference voltage Vref5, for example, the comparator Cp6outputs the low level comparison result signal Vcr6 so as to decreasethe potential of the node Nd9.

In the way described above, the comparing circuit CNL12 detects thefeedback voltage Vfb4 based on the light emission voltage Vh2 andoutputs the comparison result signal Vcr6 to adjust the output of thetransistor PD2, so that the light emission current Ih2 flowing in thelight emitting element group HS2 becomes a desired value.

The driving circuit KD2 is connected to the gate terminal G as a controlterminal of the transistor PD2 and the output terminal of the comparatorCp6 in the comparing circuit CNL12, so as to supply a drive signal Vs2as a second drive signal to the transistor PD2 in accordance with thecomparison result signal Vcr6 output from the comparator Cp6, i.e. thecomparing circuit CNL12. When receiving the low level comparison resultsignal Vcr6, for example, the driving circuit KD2 supplies the highlevel drive signal Vs2 at for example 5 V to the gate terminal G of thetransistor PD2. In this way, the transistor PD2 is turned off, and thesupply of the voltage based on the drive voltage Vk to the inductor L2is stopped. In addition, when receiving the high level comparison resultsignal Vcr6, for example, the driving circuit KD2 supplies the low leveldrive signal Vs2 at for example 0 V to the gate terminal G of thetransistor PD2. In this way, the transistor PD2 is turned on, and thevoltage based on the drive voltage Vk is supplied to the inductor L2.Note that the driving circuit KD2 may have a structure for performingthe PWM control in which the PWM signal having a predetermined dutyratio is supplied to the gate terminal G of the transistor PD2.

As described above, the dimming circuit LC12 adjusts the light emissioncurrent Ih2 output from the transistor PD2 to have a predeterminedcurrent value by the drive signal Vs2 based on the comparison resultsignal Vcr6 output from the comparing circuit CNL12, and thus adjuststhe light emission luminance of the light emitting element group HS2.

If the drive voltage Vk is lower than the light emission referencevoltage VH so that the light emission control unit HCe is required toperform the light emission stop control, the driving circuit KD1 issupplied with the low level comparison result signal Vcr1 and outputsthe high level drive signal Vs' regardless of the output of thecomparing circuit CNL11, so as to forcibly turn off the transistor PD1.In this way, the supply of the light emission current Ih1 to the lightemitting element group HS1 is stopped. In addition, if the drive voltageVk is higher than the light emission reference voltage VH so that thelight emission control unit HCe is required to perform the lightemission control, the driving circuit KD1 is supplied with the highlevel comparison result signal Vcr1 and outputs the drive signal Vs1corresponding to the output of the comparing circuit CNL11 so that thetransistor PD1 is on-off controlled. In this way, the current value ofthe light emission current Ih1 flowing in the light emitting elementgroup HS1 can be controlled by the comparison result signal Vcr5.

If the drive voltage Vk is lower than the light emission referencevoltage VH so that the light emission control unit HCe is required toperform the light emission stop control, the driving circuit KD2 issupplied with the low level comparison result signal Vcr1 and outputsthe high level drive signal Vs2 regardless of the output of thecomparing circuit CNL12 so as to forcibly turn off the transistor PD2.In this way, the supply of the light emission current Ih2 to the lightemitting element group HS2 is stopped. In addition, if the drive voltageVk is higher than the light emission reference voltage VH so that thelight emission control unit HCe is required to perform the lightemission control, the driving circuit KD2 is supplied with the highlevel comparison result signal Vcr2 and outputs the drive signal Vs2corresponding to the output of the comparing circuit CNL12 so that thetransistor PD2 is on-off controlled. In this way, the current value ofthe light emission current Ih2 flowing in the light emitting elementgroup HS2 can be controlled by the comparison result signal Vcr6.

As described above, in the lighting device 30 c according to the thirdvariation of the third embodiment of the present invention, the lightemission control unit HCe detects a magnitude relationship between thedrive voltage Vk and the light emission reference voltage VH, performslight emission control to cause light emission of the light emittingelement groups HS if the drive voltage Vk is higher than the lightemission reference voltage VH, and performs light emission stop controlto stop light emission of the light emitting element groups HS if thedrive voltage Vk is lower than the light emission reference voltage VH.Therefore, it is possible to prevent a variation in timing of causing aswell as stopping light emission of the light emitting element group HS1and the light emitting element group HS2.

Note that in the above description, an asynchronous rectifier typestep-down converter using the rectifier diodes D1 and D2 is exemplifiedas the lighting device 30 c, but this is not a limitation. It ispossible to use a synchronous rectifier type step-down converter. Inaddition, without limiting to step-down converter, a step-up convertermay be used, or a step-up and down converter may be used.

In addition, PMOS transistors are used as the transistor PD1 and thetransistor PD2 in the lighting device 30 c, but it is possible to useNMOS transistors as them. In this case, when receiving the low levelcomparison result signal Vcr5, the driving circuit KD1 should supply thelow level drive signal Vs1 at for example 0 V to the gate terminal G ofthe transistor PD1, and when receiving the high level comparison resultsignal Vcr5, the driving circuit KD1 should supply the high level drivesignal Vs1 at for example 5 V to the gate terminal G of the transistorPD1. In addition, when receiving the low level comparison result signalVcr6, the driving circuit KD2 should supply the low level drive signalVs2 at for example 0 V to the gate terminal G of the transistor PD2, andwhen receiving the high level comparison result signal Vcr6, the drivingcircuit KD2 should supply the high level drive signal Vs2 at for example5 V to the gate terminal G of the transistor PD2. Note that when an NMOStransistor is used as the transistor PD1, the driving circuit KD1 maystep up the comparison result signal Vc5 to generate the drive signalVs1, and when an NMOS transistor is uses as the transistor PD2, thedriving circuit KD2 may step up the comparison result signal Vc6 togenerate the drive signal Vs2.

Fourth Embodiment

FIG. 13 is a diagram illustrating a lighting device 40 according to afourth embodiment of the present invention. The lighting device 40includes the power supply circuit VS, light emitting element groups HSB,a semiconductor chip IC1 as a first semiconductor chip, and asemiconductor chip IC1 a as a second semiconductor chip. Note that inthe lighting device 40 illustrated in FIG. 13, the same structure as inthe lighting device 10 illustrated in FIG. 1 or in the lighting device10 a illustrated in FIG. 3 is denoted by the same numeral or symbol, anddescription thereof is appropriately omitted.

The light emitting element groups HSB include the light emitting elementgroups HS, and a light emitting element groups HSa. The light emittingelement groups HS include the light emitting element group HS1, and thelight emitting element group HS2 as a first light emitting elementgroup. The light emitting element groups HSa include a light emittingelement group HS11, and a light emitting element group HS12 as a secondlight emitting element group.

Here, the “first light emission voltage” recited in the claimscorresponds to the light emission voltage Vh2, the “first light emissionreference voltage” corresponds to the light emission reference voltageVH2, the “first light emission current” corresponds to the lightemission current Ih2, and the “first light emitting element” correspondsto the light emitting element HS2 a.

The light emitting element group HS11 includes a plurality of lightemitting elements HS11 a connected in series to each other, and aresistor element Rh11. The light emitting elements HS11 a is a lightemitting diode (LED) and is a self light emitting element. The cathodeof the light emitting elements HS11 a as one terminal of the lightemitting element group HS11 is connected to one terminal of the resistorelement Rh11. The other terminal of the resistor element Rh11 isconnected to the power supply VSS of for example 0 V that is lower thanthe drive voltage Vk. Note that the light emitting elements HS1 a is notlimited to a LED, and a general organic electro luminescence (EL)element as a self light emitting element such as a light emittingpolymer can be used.

The light emitting element group HS11 emits light when a light emissionvoltage Vh11 equal to or higher than a light emission reference voltageVH11 based on the drive voltage Vk is applied to the anode of the lightemitting elements HS1 a as the other terminal of itself, so that a lightemission current Ih11 flows in each of the light emitting elements HS11a. Note that the current value of the light emission current Ih11 isdetermined based on a resistance value of the resistor element Rh11. Inaddition, each of the light emitting elements HS1 a has an internalresistance, and a forward voltage of one light emitting element HS11 ais supposed to be 2 V, for example.

Here, in this embodiment, the light emission reference voltage VH11 forthe light emitting element group HS11 to emit light is 8 V, for example,because the light emitting element group HS11 includes four lightemitting elements HS11 a connected in series, each of which has aforward voltage of 2 V. In other words, in order that the light emittingelement group HS11 emits light, the light emission voltage Vh11 appliedto the anode of the light emitting elements HS11 a on the other terminalmust be 8 V or higher.

Here, “the anode of the light emitting elements HS11 a as the otherterminal of the light emitting element group HS11” is referred to as anode Nh11, and “the cathode of the light emitting elements HS11 a as theone terminal of the light emitting element group HS11” is referred to asa node Nh11 a. In addition, “the light emission current Ih11 flowing ineach of the light emitting elements HS11 a” is referred to as “the lightemission current Ih11 flowing in the light emitting element group HS11”.

The light emitting element group HS12 includes a plurality of lightemitting elements HS12 a as a second light emitting elements connectedin series, and a resistor element Rh12. The light emitting element HS12a is a light emitting diode (LED) and is a self light emitting element.The cathode of the light emitting elements HS12 a as one terminal of thelight emitting element group HS12 is connected to one terminal of theresistor element Rh12. The other terminal of the resistor element Rh12is connected to the power supply VSS. Note that the light emittingelement HS12 a is not limited to an LED, and a general organic electroluminescence (EL) element as a self light emitting element such as alight emitting polymer can be used.

The light emitting element group HS12 emits light when the lightemission voltage Vh12 as a second light emission voltage based on thedrive voltage Vk, which is equal to or higher than a light emissionreference voltage VH12 as a second light emission reference voltagehigher than the light emission reference voltage VH11, is applied to theanode of the light emitting elements HS12 a as the other terminal ofitself, so that a light emission current Ih12 as a second light emissioncurrent flows in each of the light emitting elements HS12 a. Note thatthe current value of the light emission current Ih12 is determined basedon the resistance value of the resistor element Rh12. In addition, eachof the light emitting elements HS12 a has an internal resistance, and aforward voltage of one light emitting element HS12 a is supposed to be 2V, for example.

Here, in this embodiment, the light emission reference voltage VH12 forthe light emitting element group HS12 to emit light is 10 V, forexample, because the light emitting element group HS12 includes fivelight emitting elements HS12 a connected in series, each of which has aforward voltage of 2 V. In other words, in order that the light emittingelement group HS12 emits light, the light emission voltage Vh12 appliedto the anode of the light emitting element HS12 a on the other terminalmust be 10 V or higher.

Here, “the anode of the light emitting element HS12 as the otherterminal of the light emitting element group HS12” is referred to as anode Nh12, and “the cathode of the light emitting element HS12 a as theone terminal of the light emitting element group HS12” is referred to asa node Nh12 a. In addition, “the light emission current Ih12 flowing ineach of the light emitting elements HS12 a” is referred to as “the lightemission current Ih12 flowing in the light emitting element group HS12”.

Here, in this embodiment, in order that the light emitting elementgroups HSa emit light without an internal variation, i.e. in order thatthe light emitting element group HS11 and the light emitting elementgroup HS12 emit light at the same time, because the light emissionreference voltage VH12 at 10 V is higher than the light emissionreference voltage VH11 at 8 V, a voltage higher than 10 V as the lightemission reference voltage VH12 must be applied to the light emittingelement groups HSa as a light emission voltage Vha. Here, the voltagefor the light emitting element groups HSa to emit light without aninternal variation is referred to as a light emission reference voltageVHa. The light emitting element groups HSa emit light when being appliedwith the light emission voltage Vha equal to or higher than the lightemission reference voltage VHa based on the light emission referencevoltage VH12. Note that in this embodiment, the light emission referencevoltage VHa is 10 V that is the same as the light emission referencevoltage VH12.

Note that in this embodiment, the light emitting element group HS12 isequipped with more number of light emitting elements HS12 a than thenumber of light emitting elements HS11 a disposed in the light emittingelement group HS11, as an example, but this is not a limitation. Inother words, the lighting device 40 according to the present inventionachieves outstanding effects in cases where the light emission referencevoltage VH11 necessary for the light emitting element group HS11 to emitlight is different from the light emission reference voltage VH12necessary for the light emitting element group HS12 to emit light, and acase where the light emitting element group HS11 and the light emittingelement group HS12 have the same number of light emitting elements isnot excluded. In addition, in the same manner, each of the lightemitting element group HS11 and the light emitting element group HS12may have a single LED.

Here, if the light emitting element groups HSa are applied with thelight emission voltage Vha, which is equal to or higher than the lightemission reference voltage VH11 and lower than or equal to the lightemission reference voltage VH12 without any control, the light emittingelement group HS11 emits light while the light emitting element groupHS12 does not emit light. In addition, after that, when the lightemission voltage Vha becomes equal to or higher than the light emissionreference voltage VH12 and is applied to the light emitting elementgroups HSa, not only the light emitting element group HS11 but also thelight emitting element group HS12 emits light. In other words, if thelight emitting element groups HSa are applied with the light emissionvoltage Vh lower than the light emission reference voltage VH12, lightemission timing is varied between the light emitting element group HS11and the light emitting element group HS12, and hence light emission ofthe entire light emitting element groups HSa may be fluctuated. Inparticular, when being used as an in-vehicle exterior lamp, thefluctuation in light emission of the light emitting element groups maycause an accident. The lighting device 40 according to the presentinvention is aimed to prevent occurrence of such a problem.

Here, in this embodiment, in order that the light emitting elementgroups HSB emit light without an internal variation, i.e. in order thatthe light emitting element groups HS and the light emitting elementgroups HSa emit light at the same time, because the light emissionreference voltage VH12 at 10 V is higher than the light emissionreference voltage VH2 at 8 V, a voltage higher than 10 V as the lightemission reference voltage VH12 must be applied to the light emittingelement groups HS as the light emission voltage Vh and must be appliedto the light emitting element groups HSa as the light emission voltageVha. Here, the voltage for the light emitting element groups HSB to emitlight without an internal variation is referred to as a light emissionreference voltage VHB. The light emitting element groups HSB emit lightwhen the light emitting element groups HS are applied with the lightemission voltage Vh equal to or higher than the light emission referencevoltage VHB based on the light emission reference voltage VH12 and thelight emitting element groups HSa are applied with the light emissionvoltage Vha equal to or higher than the light emission reference voltageVHB. Note that in this embodiment, the light emission reference voltageVHB is 10 V that is the same as the light emission reference voltageVH12.

Note that in this embodiment, the light emitting element group HS12includes more number of light emitting elements HS12 a than the numberof light emitting elements HS2 a disposed in the light emitting elementgroup HS2, as an example, but this is not a limitation. In other words,the lighting device 40 according to the present invention achievesoutstanding effects in cases where the light emission reference voltageVH2 necessary for the light emitting element group HS2 to emit light isdifferent from the light emission reference voltage VH12 necessary forthe light emitting element group HS12 to emit light, and a case wherethe light emitting element group HS2 and the light emitting elementgroup HS12 include the same number of light emitting elements is notexcluded. In addition, in the same manner, each of the light emittingelement group HS2 and the light emitting element group HS12 may have asingle LED.

Here, if the light emitting element groups HS is applied with the lightemission voltage Vh that is equal to or higher than the light emissionreference voltage VH2 and is lower than or equal to the light emissionreference voltage VH12, and the light emitting element groups HSa isapplied with the light emission voltage Vha that is equal to or higherthan the light emission reference voltage VH2 and is lower than or equalto the light emission reference voltage VH12, without any control, thenthe light emitting element group HS2 emits light while the lightemitting element group HS12 does not emit light. In addition, afterthat, when the light emission voltage Vha becomes equal to or higherthan the light emission reference voltage VH12 and is applied to thelight emitting element groups HSa, not only the light emitting elementgroup HS2 but also the light emitting element group HS12 emits light. Inother words, if the light emitting element groups HSa is applied withthe light emission voltage Vh lower than the light emission referencevoltage VH12, light emission timing is varied between the light emittingelement group HS2 and the light emitting element group HS12, and hencelight emission of the entire light emitting element groups HSB may befluctuated. In particular, when being used as an in-vehicle exteriorlamp, the fluctuation in light emission of the light emitting elementgroups may cause an accident. The lighting device 40 according to thepresent invention is aimed to prevent occurrence of such a problem.

The semiconductor chip IC1 has electrode pads for external electricconnection, which include an electrode pad T1, an electrode pad T2, anelectrode pad T3, an electrode pad T4, and an electrode pad T5. Inaddition, the semiconductor chip IC1 includes a light emission controlunit HC1 as the first light emission control unit, the dimming circuitLC1, and the dimming circuit LC2 as a first dimming portion.

The electrode pad T1 is connected to the power supply circuit VS viawiring W1 as first power supply wiring. In other words, the wiring W1 isconnected to the power supply circuit VS and the semiconductor chip IC1.The electrode pad T2 is connected to the node Nh1 of the light emittingelement group HS1. The electrode pad T3 is connected to the node Nh2 ofthe light emitting element group HS2. The electrode pad T4 is connectedto the power supply VSS.

The light emission control unit HC1 includes the comparing circuit CN asa first comparing circuit, the transistor P1 as a first control switch,and a transistor P8 as a third control switch.

The comparing circuit CN is connected to the electrode pad T1, i.e., isconnected to the power supply circuit VS via the electrode pad T1. Thecomparing circuit CN determines whether the drive voltage Vk is higheror lower than a voltage based on the light emission reference voltageVHa and outputs a result of the comparison as the comparison resultsignal Vcr1.

The transistor P1 is a PMOS transistor, which has the source terminal Sconnected to the electrode pad T1, i.e. connected to the power supplycircuit VS via the electrode pad T1, the drain terminal D connected toone terminal of the dimming circuit LC1 and one terminal of the dimmingcircuit LC2, and the gate terminal G connected to the electrode pad T5.

The transistor P8 is a PMOS transistor, which has the source terminal Sconnected to the comparing circuit CN, and the drain terminal Dconnected to the gate terminal G of the transistor P1 and the electrodepad T5. In this way, the comparing circuit CN and the gate terminal G ofthe transistor P1 are connected to each other via the transistor P8, andthe electric connection between the comparing circuit CN and the gateterminal G of the transistor P1 is controlled by the transistor P8. Inaddition, the transistor P8 has the gate terminal G connected to theelectrode pad T4, i.e. connected to the power supply VSS via theelectrode pad T4. In this way, the transistor P8 is turned on when thedrive voltage Vk is increased, and the signal level of the comparisonresult signal Vcr1, which is output from the comparing circuit CN and issupplied to the source terminal S of the transistor P8, is increased, sothat the gate-source voltage of the transistor P8 becomes equal to orhigher than a threshold voltage. Here, the connection node between thedrain terminal D of the transistor P8 and the gate terminal G of thetransistor P1 is referred to as a node Nd10.

The dimming circuit LC1 has one terminal connected to the drain terminalD of the transistor P1 in the light emission control unit HC. Inaddition, the dimming circuit LC1 has the other terminal connected tothe electrode pad T2, i.e. connected to the node Nh1 of the lightemitting element group HS1 via the electrode pad T2.

The dimming circuit LC2 has one terminal connected to the drain terminalD of the transistor P1 in the light emission control unit HC. Inaddition, the dimming circuit LC2 has the other terminal connected tothe electrode pad T3, i.e. connected to the node Nh2 of the lightemitting element group HS2 via the electrode pad T3.

The semiconductor chip IC1 a has the same structure as the semiconductorchip IC1. However, in the semiconductor chip IC1 a of FIG. 13, forconvenience of description, in order to discriminate from thesemiconductor chip IC1, the suffix “a” is added to the numeral or symbolof the structure in the semiconductor chip IC1. In addition, in thesemiconductor chip IC1 a, description of the structure described in thesemiconductor chip IC1 is appropriately omitted. Note that the“comparing circuit CN” is referred to as a “comparing circuit CNaa”here, in order to discriminate from the “comparing circuit CNa”illustrated in FIG. 5 or the like.

The semiconductor chip IC1 a has electrode pads for external electricconnection, which include an electrode pad T1 a, an electrode pad T2 a,an electrode pad T3 a, an electrode pad T4 a, and an electrode pad T5 a.In addition, the semiconductor chip IC1 a includes a light emissioncontrol unit HC1 a as a second light emission control unit, a dimmingcircuit LC1 a, and a dimming circuit LC2 a as a second dimming portion.The light emission control unit HC1 a includes the comparing circuitCNaa as a second comparing circuit, a transistor P1 a as a secondcontrol switch, and a transistor P8 a.

The electrode pad T1 a is connected to the power supply circuit VS viawiring W2 as second power supply wiring. In other words, the wiring W2is connected to the power supply circuit VS and the semiconductor chipIC1 a. The electrode pad T2 a is connected to the node Nh11 of the lightemitting element group HS11. The electrode pad T3 a is connected to thenode Nh12 of the light emitting element group HS12. Note that the wiringW2 has a wiring resistance smaller than that of the wiring W1, forexample.

The dimming circuit LC1 a has one terminal connected to the drainterminal D of the transistor P1 a of the light emission control unit HC1a. In addition, the dimming circuit LC1 a has the other terminalconnected to the electrode pad T2 a, and thus is connected to the nodeNh11 of the light emitting element group HS11 via the electrode pad T2a.

The dimming circuit LC2 a has one terminal connected to the drainterminal D of the transistor P1 a in the light emission control unit HC1a. In addition, the dimming circuit LC2 a has the other terminalconnected to the electrode pad T3 a, and thus is connected to the nodeNh12 of the light emitting element group HS12 via the electrode pad T3a.

The electrode pad T4 a is connected to the power supply circuit VS. Inthis way, the gate terminal G of the transistor P8 a is always connectedto the power supply circuit VS. Therefore, the transistor P8 a is notturned on even if the voltage level of the drive voltage Vk isincreased, and is always in off state.

The electrode pad T5 a is connected to the electrode pad T5 of thesemiconductor chip IC1 via wiring W3 as first connection wiring. Inother words, the wiring W3 electrically connects the node Nd10 and anode Nd10 a. In this way, the gate terminal G of the transistor P1 andthe gate terminal G of the transistor P1 a are electrically connected.

As described above, as to the lighting device 40, in the light emissioncontrol unit HC1, the gate terminal G of the transistor P8 of thesemiconductor chip IC1 is electrically connected to the power supplyVSS, and hence the comparison result signal Vcr1 is supplied from thecomparing circuit CN to the gate terminal G of the transistor P1. Inaddition, in the light emission control unit HC1 a, the gate terminal Gof the transistor P8 a of the semiconductor chip IC1 a is electricallyconnected to the power supply circuit VS, and hence the supply of thecomparison result signal Vcr1 a from the comparing circuit CNaa to thegate terminal G of the transistor P1 a is interrupted. In addition, thegate terminal G of the transistor P1, which is connected to thecomparing circuit CN, is electrically connected to the gate terminal Gof the transistor P1 a via the wiring W3. Further, thus in the lightingdevice 40, the light emission control unit HC1 of the semiconductor chipIC1 performs the light emission control and the light emission stopcontrol of the light emitting element groups HS connected to thesemiconductor chip IC1, and the light emission control and the lightemission stop control of the light emitting element groups HSa connectedto the semiconductor chip IC1 a, i.e. performs the light emissioncontrol and the light emission stop control of the light emittingelement groups HSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CN of the semiconductor chip IC1 and the comparingcircuit CNaa of the semiconductor chip IC1 a, the lighting device 40 canprevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

In addition, as to the lighting device 40, in the case where a wiringresistance of the wiring W1 for the semiconductor chip IC1 to receivepower supply of the drive voltage Vk and the drive current Ik from thepower supply circuit VS is larger than a wiring resistance of the wiringW2 for the semiconductor chip IC1 a to receive power supply of the drivevoltage Vk and the drive current Ik from the power supply circuit VS,the light emission control unit HC1 of the semiconductor chip IC1performs the light emission control and the light emission stop controlof the light emitting element groups HS connected to the semiconductorchip IC1, and performs the light emission control and the light emissionstop control of the light emitting element groups HSa connected to thesemiconductor chip IC1 a. Therefore, even if a potential increase in thedrive voltage Vk obtained by the comparing circuit CN of thesemiconductor chip IC1 is delayed from a potential increase in the drivevoltage Vk obtained by the comparing circuit CNaa of the semiconductorchip IC1 a based on a wiring resistance difference between the wiring W1and the wiring W2, it is possible to prevent a light emission timingvariation between the light emitting element groups HS and the lightemitting element groups HSa.

First Variation of Fourth Embodiment

FIG. 14 is a diagram illustrating a lighting device 40 a according to afirst variation of the fourth embodiment of the present invention. Thelighting device 40 a includes the power supply circuit VS, the lightemitting element groups HSB, the semiconductor chip IC1, and thesemiconductor chip IC1 a. Note that in the lighting device 40 aillustrated in FIG. 14, the same structure as in the lighting device 40illustrated in FIG. 13 is denoted by the same numeral or symbol, anddescription thereof is appropriately omitted.

The lighting device 40 a is substantially different from the lightingdevice 40 in the connection destination of the electrode pad T4 of thesemiconductor chip IC1 and in the connection destination of theelectrode pad T4 a of the semiconductor chip IC1 a.

The electrode pad T4 is connected to the power supply circuit VS. Inthis way, in the transistor P8, the gate terminal G is always connectedto the power supply circuit VS. Therefore, the transistor P8 is notturned on even if the voltage level of the drive voltage Vk isincreased, and is always in off state.

In addition, the electrode pad T4 a is connected to the power supplyVSS. In this way, in the transistor P8 a, the gate terminal G isconnected to the power supply VSS. Therefore, the transistor P8 a isturned on when the drive voltage Vk is increased so that the gate-sourcevoltage of the transistor P8 becomes equal to or higher than a thresholdvoltage.

As described above, as to the lighting device 40 a, in the lightemission control unit HC1, the gate terminal G of the transistor P8 ofthe semiconductor chip IC1 is electrically connected to the power supplycircuit VS, and hence supply of the comparison result signal Vcr1 fromthe comparing circuit CN to the gate terminal G of the transistor P1 isinterrupted. In addition, in the light emission control unit HC1 a, thegate terminal G of the transistor P8 a of the semiconductor chip IC1 ais electrically connected to the power supply VSS, and hence thecomparison result signal Vcr1 a is supplied from the comparing circuitCNaa to the gate terminal G of the transistor P1 a. In addition, thegate terminal G of the transistor P1 a connected to the comparingcircuit CNaa is electrically connected to the gate terminal G of thetransistor P1 via the wiring W3. Further, thus in the lighting device40, the light emission control unit HC1 a of the semiconductor chip IC1a performs the light emission control and the light emission stopcontrol of the light emitting element groups HS connected to thesemiconductor chip IC1, and the light emission control and the lightemission stop control of the light emitting element groups HSa connectedto the semiconductor chip IC1 a, i.e. performs the light emissioncontrol and the light emission stop control of the light emittingelement groups HSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CN of the semiconductor chip IC1 and the comparingcircuit CNaa of the semiconductor chip IC1 a, the lighting device 40 acan prevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

Note that the light emission control and the light emission stop controlin the lighting device including the semiconductor chip IC1 and thesemiconductor chip IC1 a are performed by one of the light emissioncontrol unit HC1 of the semiconductor chip IC1 and the light emissioncontrol unit HC1 a of the semiconductor chip IC1 a as described above.

Second Variation of Fourth Embodiment

FIG. 15 is a diagram illustrating a lighting device 40 b according to asecond variation of the fourth embodiment of the present invention. Thelighting device 40 b includes the power supply circuit VS, the lightemitting element groups HSB, a semiconductor chip IC2 as the firstsemiconductor chip, and a semiconductor chip IC2 a as the secondsemiconductor chip. Note that in the lighting device 40 b illustrated inFIG. 15, the same structure as in the lighting device 10 b illustratedin FIG. 4 or the lighting device 40 illustrated in FIG. 13 is denoted bythe same numeral or symbol, and description thereof is appropriatelyomitted.

The semiconductor chip IC2 has electrode pads for external electricconnection, which include the electrode pad T1, the electrode pad T2,the electrode pad T3, the electrode pad T4, and the electrode pad T5. Inaddition, the semiconductor chip IC2 includes a light emission controlunit HC2 as the first light emission control unit, the dimming circuitLC1, and the dimming circuit LC2 as the first dimming portion.

The electrode pad T1 is connected to the power supply circuit VS via thewiring W1 as the first power supply wiring. In other words, the wiringW1 is connected to the power supply circuit VS and the semiconductorchip IC2. The electrode pad T2 is connected to the node Nh1 of the lightemitting element group HS1. The electrode pad T3 is connected to thenode Nh2 of the light emitting element group HS2. The electrode pad T4is connected to the power supply VSS.

The light emission control unit HC2 includes the comparing circuit CN asthe first comparing circuit, the transistor P2, the transistor P3 as thefirst control switch, and a transistor P9 as the third control switch.

The dimming circuit LC1 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1.

The dimming circuit LC2 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1.

The transistor P2 is a PMOS transistor, which has the source terminal Sconnected to the other terminal of the dimming circuit LC1, and thedrain terminal D connected to the electrode pad T2, i.e. connected tothe node Nh1 of the light emitting element group HS1 via the electrodepad T2.

The transistor P3 is a PMOS transistor, which has the source terminal Sconnected to the other terminal of the dimming circuit LC2, and thedrain terminal D connected to the electrode pad T3, i.e. connected tothe node Nh2 of the light emitting element group HS2 via the electrodepad T3.

The transistor P9 is a PMOS transistor, which has the source terminal Sconnected to the comparing circuit CN, and the drain terminal Dconnected to the gate terminal G of the transistor P1 and the electrodepad T5. In this way, the comparing circuit CN is connected to the gateterminals G of the transistor P2 and the transistor P3 via thetransistor P9, and the electric connection between the comparing circuitCN and the gate terminals G of the transistor P2 and the transistor P3is controlled by the transistor P9. In addition, the transistor P9 hasthe gate terminal G connected to the electrode pad T4, i.e. connected tothe power supply VSS via the electrode pad T4. In this way, thetransistor P9 is turned on when the drive voltage Vk is increased sothat the signal level of the comparison result signal Vcr1, which isoutput from the comparing circuit CN and is supplied to the sourceterminal S of the transistor P9, is increased, and hence the gate-sourcevoltage of the transistor P9 becomes equal to or higher than a thresholdvoltage. Here, the connection node between the drain terminal D of thetransistor P9 and the gate terminals G of the transistor P2 and thetransistor P3 is referred to as a node Nd11.

The semiconductor chip IC2 a has the same structure as the semiconductorchip IC2. However, in the semiconductor chip IC2 a of FIG. 15, forconvenience of description, in order to discriminate from thesemiconductor chip IC2, the suffix “a” is added to the numeral or symbolof the structure in the semiconductor chip IC2. In addition, in thesemiconductor chip IC2 a, description of the structure described in thesemiconductor chip IC2 is appropriately omitted. Note that the“comparing circuit CN” is referred to as a “comparing circuit CNaa”here, in order to discriminate from the “comparing circuit CNa”illustrated in FIG. 5 or the like.

The semiconductor chip IC2 a has electrode pads for external electricconnection, which include the electrode pad T1 a, the electrode pad T2a, the electrode pad T3 a, the electrode pad T4 a, and the electrode padT5 a. In addition, the semiconductor chip IC2 a includes a lightemission control unit HC2 a as the second light emission control unit,the dimming circuit LC1 a, and the dimming circuit LC2 a as the seconddimming portion. The light emission control unit HC2 a includes thecomparing circuit CNaa, a transistor P2 a as the second control switch,a transistor P3 a as the second control switch, and a transistor P9 a.

The electrode pad T1 a is connected to the power supply circuit VS viathe wiring W2 as the second power supply wiring. In other words, thewiring W2 is connected to the power supply circuit VS and thesemiconductor chip IC2 a. The electrode pad T2 a is connected to thenode Nh11 of the light emitting element group HS11. The electrode pad T3a is connected to the node Nh12 of the light emitting element groupHS12. Note that the wiring W2 has a smaller wiring resistance than thewiring W1, for example.

The dimming circuit LC1 a has one terminal connected to the electrodepad T1 a, i.e. connected to the power supply circuit VS via theelectrode pad T1 a.

The dimming circuit LC2 a has one terminal connected to the electrodepad T1 a, i.e. connected to the power supply circuit VS via theelectrode pad T1 a.

The transistor P2 a is a PMOS transistor, which has the source terminalS connected to the other terminal of the dimming circuit LC1 a, and thedrain terminal D connected to the electrode pad T2 a, i.e. connected tothe node Nh11 of the light emitting element group HS11 via the electrodepad T2 a.

The transistor P3 a is a PMOS transistor, which has the source terminalS connected to the other terminal of the dimming circuit LC2 a, and thedrain terminal D connected to the electrode pad T3 a, i.e. connected tothe node Nh12 of the light emitting element group HS12 via the electrodepad T3 a.

The electrode pad T4 a is connected to the power supply circuit VS. Inthis way, in the transistor P9 a, the gate terminal G is alwaysconnected to the power supply circuit VS. Therefore, transistor P9 a isnot turned on even if the voltage level of the drive voltage Vk isincreased, and is always in off state.

The electrode pad T5 a is connected to the electrode pad T5 of thesemiconductor chip IC2 via the wiring W3. In other words, the wiring W3electrically connects the node Nd11 and the node Nd11 a. In this way,the gate terminals G of the transistor P2 and the transistor P3 areelectrically connected to gate terminals G of the transistor P2 and thetransistor P3 a.

As described above, in the lighting device 40 b, the gate terminal G ofthe transistor P9 of the semiconductor chip IC2 is electricallyconnected to the power supply VSS in the light emission control unitHC2, and hence the comparison result signal Vcr1 is supplied from thecomparing circuit CN to the gate terminals G of the transistor P2 andthe transistor P3. In addition, the gate terminals G of the transistorP2 a and the transistor P3 a of the semiconductor chip IC2 a areelectrically connected to the power supply circuit VS in the lightemission control unit HC2 a, and hence the supply of the comparisonresult signal Vcr1 a from the comparing circuit CNaa to the gateterminals G of the transistor P2 a and the transistor P3 a isinterrupted. In addition, the gate terminals G of the transistor P2 andthe transistor P3, which are connected to the comparing circuit CN, areelectrically connected to the gate terminals G of the transistor P2 aand the transistor P3 a via the wiring W3. Further, in this way, in thelighting device 40 b, the light emission control unit HC2 of thesemiconductor chip IC2 performs the light emission control and the lightemission stop control of the light emitting element groups HS connectedto the semiconductor chip IC2, and the light emission control and thelight emission stop control of the light emitting element groups HSaconnected to the semiconductor chip IC2 a, i.e. performs the lightemission control and the light emission stop control of the lightemitting element groups HSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CN of the semiconductor chip IC2 and the comparingcircuit CNaa of the semiconductor chip IC2 a, the lighting device 40 bcan prevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

In addition, as to the lighting device 40 b, in the case where a wiringresistance of the wiring W1 for the semiconductor chip IC2 to receivepower supply of the drive voltage Vk and the drive current Ik from thepower supply circuit VS is larger than a wiring resistance of the wiringW2 for the semiconductor chip IC2 a to receive power supply of the drivevoltage Vk and the drive current Ik from the power supply circuit VS,the light emission control unit HC2 of the semiconductor chip IC2performs the light emission control and the light emission stop controlof the light emitting element groups HS connected to the semiconductorchip IC2, and performs the light emission control and the light emissionstop control of the light emitting element groups HSa connected to thesemiconductor chip IC2 a. Therefore, even if a potential increase in thedrive voltage Vk obtained by the comparing circuit CN of thesemiconductor chip IC2 is delayed from a potential increase in the drivevoltage Vk obtained by the comparing circuit CNaa of the semiconductorchip IC2 a, based on the wiring resistance difference between the wiringW1 and the wiring W2, it is possible to prevent a light emission timingvariation between the light emitting element groups HS and the lightemitting element groups HSa.

Third Variation of Fourth Embodiment

FIG. 16 is a diagram illustrating a lighting device 40 c according to athird variation of the fourth embodiment of the present invention. Thelighting device 40 c includes the power supply circuit VS, the lightemitting element groups HSB, the semiconductor chip IC2, and thesemiconductor chip IC2 a. Note that in the lighting device 40 cillustrated in FIG. 16, the same structure as in the lighting device 40b illustrated in FIG. 15 is denoted by the same numeral or symbol, anddescription thereof is appropriately omitted.

The lighting device 40 c is substantially different from the lightingdevice 40 b in the connection destination of the electrode pad T4 of thesemiconductor chip IC2 and in the connection destination of theelectrode pad T4 a of the semiconductor chip IC2 a.

The electrode pad T4 is connected to the power supply circuit VS. Inthis way, on the transistor P9, the gate terminal G is always connectedto the power supply circuit VS. Therefore, transistor P9 is not turnedon even if the voltage level of the drive voltage Vk is increased, andis always in off state.

In addition, the electrode pad T4 a is connected to the power supplyVSS. In this way, in the transistor P9 a, the gate terminal G isconnected to the power supply VSS. Therefore, transistor P9 a is turnedon when the drive voltage Vk is increased so that the gate-sourcevoltage of the transistor P9 becomes equal to or higher than a thresholdvoltage.

As described above, in the lighting device 40 a, the gate terminal G ofthe transistor P9 of the semiconductor chip IC2 is electricallyconnected to the power supply circuit VS in the light emission controlunit HC2, and hence supply of the comparison result signal Vcr1 from thecomparing circuit CN to the gate terminals G of the transistor P2 andthe transistor P3 is interrupted. In addition, in the light emissioncontrol unit HC2 a, the gate terminal G of the transistor P9 a of thesemiconductor chip IC2 a is electrically connected to the power supplyVSS, and hence supply of the comparison result signal Vcr1 a from thecomparing circuit CNaa to the gate terminals G of the transistor P2 aand the transistor P3 a is performed. In addition, the gate terminals Gof the transistor P2 a and the transistor P3 a connected to thecomparing circuit CNaa are electrically connected to the gate terminalsG of the transistor P2 and the transistor P3 via the wiring W3. Further,in this way, in the lighting device 40 c, the light emission controlunit HC2 a of the semiconductor chip IC2 a performs the light emissioncontrol and the light emission stop control of the light emittingelement groups HS connected to the semiconductor chip IC2, and the lightemission control and the light emission stop control of the lightemitting element groups HSa connected to the semiconductor chip IC2 a,i.e. performs the light emission control and the light emission stopcontrol of the light emitting element groups HSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CN of the semiconductor chip IC2 and the comparingcircuit CNaa of the semiconductor chip IC2 a, the lighting device 40 ccan prevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

Note that the light emission control and the light emission stop controlof the lighting device including the semiconductor chip IC2 and thesemiconductor chip IC2 a are performed by one of the light emissioncontrol unit HC2 of the semiconductor chip IC2 and the light emissioncontrol unit HC2 a of the semiconductor chip IC2 a, as described above.

Fourth Variation of Fourth Embodiment

FIG. 17 is a diagram illustrating a lighting device 40 d according to afourth variation of the fourth embodiment of the present invention. Thelighting device 40 d includes the power supply circuit VS, the lightemitting element groups HSB, a semiconductor chip IC3 as the firstsemiconductor chip, and a semiconductor chip IC3 a as the secondsemiconductor chip. Note that in the lighting device 40 d illustrated inFIG. 17, the same structure as in the lighting device 20 illustrated inFIG. 5, the lighting device 20 a illustrated in FIG. 7, or the lightingdevice 40 illustrated in FIG. 13 is denoted by the same numeral orsymbol, and description thereof is appropriately omitted.

The semiconductor chip IC3 has electrode pads for external electricconnection, which include the electrode pad T1, the electrode pad T2,the electrode pad T3, the electrode pad T4, the electrode pad T5, theelectrode pad T6, and the electrode pad T7. In addition, thesemiconductor chip IC3 includes a light emission control unit HC3 as thefirst light emission control unit, the dimming circuit LC1, and thedimming circuit LC2 as the first dimming portion.

The light emission control unit HC3 includes the comparing circuit CNaas the first comparing circuit, the transistor N1, the transistor N2 asthe first control switch, and a transistor P10 as the third controlswitch.

The comparing circuit CNa is connected to the electrode pad T1, i.e. isconnected to the power supply circuit VS via the electrode pad T1. Thecomparing circuit CNa determines whether the drive voltage Vk is higheror lower than the light emission reference voltage VHa or a voltagebased on the light emission reference voltage VHa, and outputs a resultof the comparison as the comparison result signal Vcr2.

The dimming circuit LC1 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1, and the other terminal connected to the electrode pad T2.

The dimming circuit LC2 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1, and the other terminal connected to the electrode pad T3.

The transistor N1 is an NMOS transistor, which has the source terminal Sconnected to the power supply VSS, and the drain terminal D connected tothe electrode pad T6.

The transistor N2 is an NMOS transistor, which has the source terminal Sconnected to the power supply VSS, and the drain terminal D connected tothe electrode pad T7.

The transistor P10 is a PMOS transistor, which has the source terminal Sconnected to the comparing circuit CNa, and the drain terminal Dconnected to the gate terminals G of the transistor N1 and thetransistor N2 and the electrode pad T5. In this way, the comparingcircuit CNa is connected to the gate terminals G of the transistor N1and the transistor N2 via the transistor P10, and the electricconnection between the comparing circuit CNa and the gate terminals G ofthe transistor N1 and the transistor N2 is controlled by the transistorP10. In addition, the transistor P10 has the gate terminal G connectedto the electrode pad T4, i.e. connected to the power supply VSS via theelectrode pad T4. In this way, the transistor P10 is turned on when thedrive voltage Vk is increased, and the signal level of the comparisonresult signal Vcr2, which is output from the comparing circuit CNa andis supplied to the source terminal S of the transistor P10, is increasedso that the gate-source voltage of the transistor P10 becomes equal toor higher than a threshold voltage. Here, the connection node betweenthe drain terminal D of the transistor P10 and the gate terminals G ofthe transistor N1 and the transistor N2 is referred to as a node Nd12.

The light emitting element groups HSB include the light emitting elementgroups HS and the light emitting element groups HSa. The light emittingelement groups HS include the light emitting element group HS1, and thelight emitting element group HS2 as the first light emitting elementgroup. The light emitting element groups HSa include the light emittingelement group HS11, and the light emitting element group HS12 as thesecond light emitting element group.

The light emitting element group HS1 has the node Nh1 connected to theelectrode pad T2, i.e. connected to the other terminal of the dimmingcircuit LC1 via the electrode pad T2, and the node Nh1 a connected tothe electrode pad T6, i.e. connected to the drain terminal D of thetransistor N1 via the electrode pad T6.

The light emitting element group HS2 has the node Nh2 connected to theelectrode pad T3, i.e. connected to the other terminal of the dimmingcircuit LC2 via the electrode pad T3, and the node NH2 a connected tothe electrode pad T7, i.e. connected to the drain terminal D of thetransistor N2 via the electrode pad T7.

The semiconductor chip IC3 a has the same structure as the semiconductorchip IC3. However, in the semiconductor chip IC3 a of FIG. 17, forconvenience of description, in order to discriminate from thesemiconductor chip IC3, the suffix “a” is added to the numeral or symbolof the structure in the semiconductor chip IC3. In addition, in thesemiconductor chip IC3 a, description of the structure described in thesemiconductor chip IC3 is appropriately omitted. Note that the“comparing circuit CNa” is referred to as a “comparing circuit CNaaa”here, in order to discriminate from the “comparing circuit CNaa”illustrated in FIG. 13 or the like.

The semiconductor chip IC3 a has electrode pads for external electricconnection, which include the electrode pad T1 a, the electrode pad T2a, the electrode pad T3 a, the electrode pad T4 a, the electrode pad T5a, an electrode pad T6 a, and an electrode pad T7 a. In addition, thesemiconductor chip IC3 a includes a light emission control unit HC3 a asthe second light emission control unit, the dimming circuit LC1 a, andthe dimming circuit LC2 a as the second dimming portion. The lightemission control unit HC3 a includes the comparing circuit CNaaa as thesecond comparing circuit, a transistor N1 a, a transistor N2 a as thesecond control switch, and a transistor P10 a.

The electrode pad T1 a is connected to the power supply circuit VS viathe wiring W2 as the second power supply wiring. In other words, thewiring W2 is connected to the power supply circuit VS and thesemiconductor chip IC3 a. The electrode pad T2 a is connected to thenode Nh11 of the light emitting element group HS11. The electrode pad T3a is connected to the node Nh12 of the light emitting element groupHS12. Note that the wiring W2 has a smaller wiring resistance than thewiring W1, for example.

The light emitting element group HS11 has the node Nh11 connected to theelectrode pad T2 a, i.e. connected to the other terminal of the dimmingcircuit LC1 a via the electrode pad T2 a. The node Nh11 a is connectedto the electrode pad T6 a, i.e. is connected to the drain terminal D ofthe transistor N1 a via the electrode pad T6 a.

The light emitting element group HS12 has the node Nh12 connected to theelectrode pad T3 a, i.e. connected to the other terminal of the dimmingcircuit LC2 a via the electrode pad T3 a. The node Nh12 a is connectedto the electrode pad T7 a, i.e. is connected to the drain terminal D ofthe transistor N2 a via the electrode pad T7 a.

The electrode pad T4 a is connected to the power supply circuit VS. Inthis way, in the transistor P10 a, the gate terminal G is alwaysconnected to the power supply circuit VS. Therefore, the transistor P10a is not turned on even if the voltage level of the drive voltage Vk isincreased, and is always in off state.

The electrode pad T5 a is connected to the electrode pad T5 of thesemiconductor chip IC3 via the wiring W3. In other words, the wiring W3electrically connects the node Nd12 and the node Nd12 a. In this way,the gate terminals G of the transistor N1 and the transistor N2 areelectrically connected to the gate terminals G of the transistor N1 aand the transistor N2 a.

As described above, in the lighting device 40 d, the gate terminal G ofthe transistor P10 of the semiconductor chip IC3 is electricallyconnected to the power supply VSS in the light emission control unitHC3, and hence supply of the comparison result signal Vcr2 from thecomparing circuit CNa to the gate terminals G of the transistor N1 andthe transistor N2 is performed. In addition, in the light emissioncontrol unit HC3 a, the gate terminals G of the transistor N1 a and thetransistor N2 a of the semiconductor chip IC3 a are electricallyconnected to the power supply circuit VS, and hence supply of thecomparison result signal Vcr2 a from the comparing circuit CNaaa to thegate terminals G of the transistor N1 a and the transistor N2 a isinterrupted. In addition, the gate terminals G of the transistor N1 andthe transistor N2 connected to the comparing circuit CNa areelectrically connected to the gate terminals G of the transistor N1 aand the transistor N2 a via the wiring W3. Further, in this way, in thelighting device 40 d, the light emission control unit HC3 of thesemiconductor chip IC3 performs the light emission control and the lightemission stop control of the light emitting element groups HS connectedto the semiconductor chip IC3, and the light emission control and thelight emission stop control of the light emitting element groups HSaconnected to the semiconductor chip IC3 a, i.e. performs the lightemission control and the light emission stop control of the lightemitting element groups HSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CNa of the semiconductor chip IC3 and the comparingcircuit CNaaa of the semiconductor chip IC3 a, the lighting device 40 dcan prevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

In addition, in the lighting device 40 d, in a case where the wiringresistance of the wiring W1 for the semiconductor chip IC3 to receivepower supply of the drive voltage Vk and the drive current Ik from thepower supply circuit VS is larger than the wiring resistance of thewiring W2 for the semiconductor chip IC3 a to receive power supply ofthe drive voltage Vk and the drive current Ik from the power supplycircuit VS, the light emission control and the light emission stopcontrol of the light emitting element groups HS connected to thesemiconductor chip IC3, and the light emission control and the lightemission stop control of the light emitting element groups HSa connectedto the semiconductor chip IC3 a are performed by the light emissioncontrol unit HC3 of the semiconductor chip IC3. Therefore, even if apotential increase in the drive voltage Vk obtained by the comparingcircuit CNa of the semiconductor chip IC3 is delayed from a potentialincrease in the drive voltage Vk obtained by the comparing circuit CNaaaof the semiconductor chip IC3 a, based on the wiring resistancedifference between the wiring W1 and the wiring W2, it is possible toprevent a light emission timing variation between the light emittingelement groups HS and the light emitting element groups HSa.

Fifth Variation of Fourth Embodiment

FIG. 18 is a diagram illustrating a lighting device 40 e according to afifth variation of the fourth embodiment of the present invention. Thelighting device 40 e includes the power supply circuit VS, the lightemitting element groups HSB, the semiconductor chip IC3, and thesemiconductor chip IC3 a. Note that in the lighting device 40 eillustrated in FIG. 18, the same structure as in the lighting device 40d illustrated in FIG. 17 is denoted by the same numeral or symbol, anddescription thereof is appropriately omitted.

The lighting device 40 e is substantially different from the lightingdevice 40 d in the connection destination of the electrode pad T4 of thesemiconductor chip IC3 and in the connection destination of theelectrode pad T4 a of the semiconductor chip IC3 a.

The electrode pad T4 is connected to the power supply circuit VS. Inthis way, in the transistor P10, the gate terminal G is always connectedto the power supply circuit VS. Therefore, the transistor P10 is notturned on even if the voltage level of the drive voltage Vk isincreased, and is always in off state.

In addition, the electrode pad T4 a is connected to the power supplyVSS. In this way, in the transistor P10 a, the gate terminal G isconnected to the power supply VSS. Therefore, the transistor P10 a isturned on when the drive voltage Vk is increased so that the gate-sourcevoltage of the transistor P10 becomes equal to or higher than athreshold voltage.

As described above, in the lighting device 40 e, the gate terminal G ofthe transistor P10 of the semiconductor chip IC3 is electricallyconnected to the power supply circuit VS in the light emission controlunit HC3, and hence supply of the comparison result signal Vcr2 from thecomparing circuit CNa to the gate terminals G of the transistor N1 andthe transistor N2 is interrupted. In addition, the gate terminal G ofthe transistor P10 a of the semiconductor chip IC3 a is electricallyconnected to the power supply VSS in the light emission control unit HC3a, and hence supply of the comparison result signal Vcr2 a from thecomparing circuit CNaaa to the gate terminals G of the transistor N1 aand the transistor N2 a is performed. In addition, the gate terminals Gof the transistor N1 a and the transistor N2 a connected to thecomparing circuit CNaaa are electrically connected to the gate terminalsG of the transistor N1 and the transistor N2 via the wiring W3. Further,in this way, in the lighting device 40 e, the light emission controlunit HC3 a of the semiconductor chip IC3 a performs the light emissioncontrol and the light emission stop control of the light emittingelement groups HS connected to the semiconductor chip IC3, and the lightemission control and the light emission stop control of the lightemitting element groups HSa connected to the semiconductor chip IC3 a,i.e. performs the light emission control and the light emission stopcontrol of the light emitting element groups HSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CNa of the semiconductor chip IC3 and the comparingcircuit CNaaa of the semiconductor chip IC3 a, the lighting device 40 ecan prevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

Note that as described above, the light emission control and the lightemission stop control of the lighting device including the semiconductorchip IC3 and the semiconductor chip IC3 a are performed by one of thelight emission control unit HC3 of the semiconductor chip IC3 and thelight emission control unit HC3 a of the semiconductor chip IC3 a.

Sixth Variation of Fourth Embodiment

FIG. 19 is a diagram illustrating a lighting device 40 f according to asixth variation of the fourth embodiment of the present invention. Thelighting device 40 f includes the power supply circuit VS, the lightemitting element groups HSB, a semiconductor chip IC4 as the firstsemiconductor chip, and a semiconductor chip IC4 a as the secondsemiconductor chip. Note that in the lighting device 40 f illustrated inFIG. 19, the same structure as in the lighting device 30 illustrated inFIG. 8, the lighting device 30 a illustrated in FIG. 10, or the lightingdevice 40 illustrated in FIG. 13 is denoted by the same numeral orsymbol, and description thereof is appropriately omitted.

The semiconductor chip IC4 has electrode pads for external electricconnection, which include the electrode pad T1, the electrode pad T2,the electrode pad T3, the electrode pad T4, and the electrode pad T5. Inaddition, the semiconductor chip IC4 includes a light emission controlunit HC4 as the first light emission control unit, the dimming circuitLC1, and the dimming circuit LC2 as the first dimming portion.

The light emission control unit HC4 includes the comparing circuit CNaas the first comparing circuit, the transistor P6, the transistor P7 asthe first control switch, and a transistor P11 as the third controlswitch.

The comparing circuit CNa is connected to the electrode pad T1, i.e. isconnected to the power supply circuit VS via the electrode pad T1. Thecomparing circuit CNa determines whether the drive voltage Vk is higheror lower than a voltage based on the light emission reference voltageVH, and outputs a result of the comparison as the comparison resultsignal Vcr2.

The dimming circuit LC1 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1, and the other terminal connected to the electrode pad T2.

The dimming circuit LC2 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1, and the other terminal connected to the electrode pad T3.

The transistor P6 is a PMOS transistor, which has the source terminal Sconnected to the power supply circuit VS, and the drain terminal Dconnected to the dimming circuit LC1.

The transistor P7 is a PMOS transistor, which has the source terminal Sconnected to the power supply circuit VS, and the drain terminal Dconnected to the dimming circuit LC2.

The transistor P11 is a PMOS transistor, which has the source terminal Sconnected to the comparing circuit CNa, and the drain terminal Dconnected to the gate terminals G of the transistor P6 and thetransistor P7 and the electrode pad T5. In this way, the comparingcircuit CNa is connected to the gate terminals G of the transistor P6and the transistor P7 via the transistor P11. The electric connectionbetween the comparing circuit CNa and the gate terminals G of thetransistor P6 and the transistor P7 is controlled by the transistor P11.In addition, transistor P11 has the gate terminal G connected to theelectrode pad T4, i.e. connected to the power supply VSS via theelectrode pad T4. In this way, the transistor P11 is turned on when thedrive voltage Vk is increased, and the signal level of the comparisonresult signal Vcr2, which is output from the comparing circuit CNa andis supplied to the source terminal S of the transistor P11, increases sothat the gate-source voltage of the transistor P11 becomes equal to orhigher than a threshold voltage. Here, the connection node between thedrain terminal D of the transistor P11 and the gate terminals G of thetransistor P6 and the transistor P7 is referred to as a node Nd13.

The semiconductor chip IC4 a has the same structure as the semiconductorchip IC4. However, in the semiconductor chip IC4 a of FIG. 19, forconvenience of description, in order to discriminate from thesemiconductor chip IC4, the suffix “a” is added to the numeral or symbolof the structure in the semiconductor chip IC4. In addition, in thesemiconductor chip IC4 a, description of the structure described in thesemiconductor chip IC4 is appropriately omitted. Note that the“comparing circuit CNa” is referred to as the “comparing circuit CNaaa”here, in order to discriminate from the “comparing circuit CNaa”illustrated in FIG. 13 or the like.

The semiconductor chip IC4 a has electrode pads for external electricconnection, which include the electrode pad T1 a, the electrode pad T2a, the electrode pad T3 a, the electrode pad T4 a, and the electrode padT5 a. In addition, the semiconductor chip IC4 a includes a lightemission control unit HC4 a as the second light emission control unit,the dimming circuit LC1 a, and the dimming circuit LC2 a as the seconddimming portion. The light emission control unit HC4 a includes thecomparing circuit CNaaa as the second comparing circuit, a transistor P6a, a transistor P7 a as the second control switch, and a transistor P11a.

The dimming circuit LC11 has one terminal connected to the electrode padT1 a, i.e. connected to the power supply circuit VS via the electrodepad T1 a, and the other terminal connected to the electrode pad T2 a.

The dimming circuit LC12 has one terminal connected to the electrode padT1 a, i.e. connected to the power supply circuit VS via the electrodepad T1 a, and the other terminal connected to the electrode pad T3 a.

The electrode pad T4 a is connected to the power supply circuit VS. Inthis way, in the transistor P11 a, the gate terminal G is alwaysconnected to the power supply circuit VS. Therefore, the transistor P11a is not turned on even if the voltage level of the drive voltage Vk isincreased, and is always in off state.

The electrode pad T5 a is connected to the electrode pad T5 of thesemiconductor chip IC4 via the wiring W3. In other words, the wiring W3electrically connects the node Nd13 and the node Nd13 a. In this way,the gate terminals G of the transistor P6 and the transistor P7 areelectrically connected to the gate terminals G of the transistor P6 aand transistor P7 a.

As described above, in the lighting device 40 f, the gate terminal G ofthe transistor P11 of the semiconductor chip IC4 is electricallyconnected to the power supply VSS in the light emission control unitHC4, and hence supply of the comparison result signal Vcr2 from thecomparing circuit CNa to the gate terminals G of the transistor P6 andthe transistor P7 is performed. In addition, in the light emissioncontrol unit HC4 a, the gate terminals G of the transistor P6 a and thetransistor P7 a are electrically connected to the power supply circuitVS in the semiconductor chip IC4 a, and hence supply of the comparisonresult signal Vcr2 a from the comparing circuit CNaaa to the gateterminals G of the transistor P6 a and transistor P7 a is interrupted.In addition, the gate terminals G of the transistor P6 and thetransistor P7 connected to the comparing circuit CNa are electricallyconnected to the gate terminals G of the transistor P6 a and transistorP7 a via the wiring W3. Further, in this way, in the lighting device 40f, the light emission control unit HC4 of the semiconductor chip IC4performs the light emission control and the light emission stop controlof the light emitting element groups HS connected to the semiconductorchip IC4, and the light emission control and the light emission stopcontrol of the light emitting element groups HSa connected to thesemiconductor chip IC4 a, i.e. performs the light emission control andthe light emission stop control of the light emitting element groupsHSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CNa of the semiconductor chip IC4 and the comparingcircuit CNaaa of the semiconductor chip IC4 a, the lighting device 40 fcan prevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

In addition, in the lighting device 40 f, in a case where a wiringresistance of the wiring W1 for the semiconductor chip IC4 to receivepower supply of the drive voltage Vk and the drive current Ik from thepower supply circuit VS is larger than a wiring resistance of the wiringW2 for the semiconductor chip IC4 a to receive power supply of the drivevoltage Vk and the drive current Ik from the power supply circuit VS,the light emission control and the light emission stop control of thelight emitting element groups HS connected to the semiconductor chipIC4, and the light emission control and the light emission stop controlof the light emitting element groups HSa connected to the semiconductorchip IC4 a are performed by the light emission control unit HC4 of thesemiconductor chip IC4. Therefore, even if a potential increase in thedrive voltage Vk obtained by the comparing circuit CNa of thesemiconductor chip IC4 is delayed from a potential increase in the drivevoltage Vk obtained by the comparing circuit CNaaa of the semiconductorchip IC4 a, based on the wiring resistance difference between the wiringW1 and the wiring W2, it is possible to prevent a light emission timingvariation between the light emitting element groups HS and the lightemitting element groups HSa.

Seventh Variation of Fourth Embodiment

FIG. 20 is a diagram illustrating a lighting device 40 g according to aseventh variation of the fourth embodiment of the present invention. Thelighting device 40 g includes the power supply circuit VS, the lightemitting element groups HSB, the semiconductor chip IC4, and thesemiconductor chip IC4 a. Note that in the lighting device 40 gillustrated in FIG. 20, the same structure as in the lighting device 40f illustrated in FIG. 19 is denoted by the same numeral or symbol, anddescription thereof is appropriately omitted.

The lighting device 40 g is substantially different from the lightingdevice 40 f in the connection destination of the electrode pad T4 of thesemiconductor chip IC4 and in the connection destination of theelectrode pad T4 a of the semiconductor chip IC4 a.

The electrode pad T4 is connected to the power supply circuit VS. Inthis way, in the transistor P11, the gate terminal G is always connectedto the power supply circuit VS. Therefore, transistor P11 is not turnedon even if the voltage level of the drive voltage Vk is increased, andis always in off state.

In addition, the electrode pad T4 a is connected to the power supplyVSS. In this way, in the transistor P11 a, the gate terminal G isconnected to the power supply VSS. Therefore, the transistor P11 a isturned on when the drive voltage Vk is increased so that the gate-sourcevoltage of the transistor P11 becomes equal to or higher than athreshold voltage.

As described above, in the lighting device 40 g, the gate terminal G ofthe transistor P11 of the semiconductor chip IC4 is electricallyconnected to the power supply circuit VS in the light emission controlunit HC4, and hence supply of the comparison result signal Vcr2 from thecomparing circuit CNa to the gate terminals G of the transistor P6 andthe transistor P7 is interrupted. In addition, in the light emissioncontrol unit HC4 a, the gate terminal G of the transistor P11 a of thesemiconductor chip IC4 a is electrically connected to the power supplyVSS, and hence supply of the comparison result signal Vcr2 a from thecomparing circuit CNaaa to the gate terminals G of the transistor P6 aand transistor P7 a is performed. In addition, the gate terminals G ofthe transistor P6 a and transistor P7 a connected to the comparingcircuit CNaaa are electrically connected to the gate terminals G of thetransistor P6 and the transistor P7 via the wiring W3. Further, in thisway, in the lighting device 40 g, the light emission control unit HC4 aof the semiconductor chip IC4 a performs the light emission control andthe light emission stop control of the light emitting element groups HSconnected to the semiconductor chip IC4, and the light emission controland the light emission stop control of the light emitting element groupsHSa connected to the semiconductor chip IC4 a, i.e. performs the lightemission control and the light emission stop control of the lightemitting element groups HSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CNa of the semiconductor chip IC4 and the comparingcircuit CNaaa of the semiconductor chip IC4 a, the lighting device 40 gcan prevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

Note that as described above, in the lighting device including thesemiconductor chip IC4 and the semiconductor chip IC4 a, the lightemission control and the light emission stop control are performed byone of the light emission control unit HC4 of the semiconductor chip IC4and the light emission control unit HC4 a of the semiconductor chip IC4a.

Eighth Variation of Fourth Embodiment

FIG. 21 is a diagram illustrating a lighting device 40 h according to aneighth variation of the fourth embodiment of the present invention. Thelighting device 40 h includes the power supply circuit VS, the lightemitting element groups HSB, a semiconductor chip IC5 as the firstsemiconductor chip, and a semiconductor chip IC5 a as the secondsemiconductor chip. Note that in the lighting device 40 h illustrated inFIG. 21, the same structure as in the lighting device 30 b illustratedin FIG. 11 or the lighting device 40 illustrated in FIG. 13 is denotedby the same numeral or symbol, and description thereof is appropriatelyomitted.

The semiconductor chip IC5 has electrode pads for external electricconnection, which include the electrode pad T1, the electrode pad T2,the electrode pad T3, the electrode pad T4, and the electrode pad T5. Inaddition, the semiconductor chip IC5 includes a light emission controlunit HC5 as the first light emission control unit, the dimming circuitLC1, and the dimming circuit LC2 as the first dimming portion.

The light emission control unit HC5 includes the comparing circuit CNaas the first comparing circuit, the transistor N3, the transistor N4 asthe first control switch, and a transistor P12 as the third controlswitch.

The comparing circuit CNa is connected to the electrode pad T1, i.e. isconnected to the power supply circuit VS via the electrode pad T1. Thecomparing circuit CNa determines whether the drive voltage Vk is higheror lower than the light emission reference voltage VH or a voltage basedon the light emission reference voltage VH, and outputs a result of thecomparison as the comparison result signal Vcr2.

The dimming circuit LC1 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1, and the other terminal connected to the electrode pad T2.

The dimming circuit LC2 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1, and the other terminal connected to the electrode pad T3.

The transistor N3 is an NMOS transistor, which has the source terminal Sconnected to the power supply circuit VS, and the drain terminal Dconnected to the dimming circuit LC1.

The transistor N4 is an NMOS transistor, which has the source terminal Sconnected to the power supply circuit VS, and the drain terminal Dconnected to the dimming circuit LC2.

The transistor P12 is a PMOS transistor, which has the source terminal Sconnected to the comparing circuit CNa, and the drain terminal Dconnected to the gate terminals G of the transistor N3 and thetransistor N4 and the electrode pad T5. In this way, the comparingcircuit CNa is connected to the gate terminals G of the transistor N3and the transistor N4 via the transistor P12, and the electricconnection between the comparing circuit CNa and the gate terminals G ofthe transistor N3 and the transistor N4 is controlled by the transistorP12. In addition, the transistor P12 has the gate terminal G connectedto the electrode pad T4, i.e. connected to the power supply VSS via theelectrode pad T4. In this way, the transistor P12 is turned on when thedrive voltage Vk is increased, and the signal level of the comparisonresult signal Vcr2, which is output from the comparing circuit CNa andis supplied to the source terminal S of the transistor P12, is increasedso that the gate-source voltage of the transistor P12 becomes equal toor higher than a threshold voltage. Here, the drain terminal D of thetransistor P12 and the connection node between the gate terminals G ofthe transistor N3 and the transistor N4 is referred to as a node Nd14.

The semiconductor chip IC5 a has the same structure as the semiconductorchip IC5. However, in the semiconductor chip IC5 a of FIG. 21, forconvenience of description, in order to discriminate from thesemiconductor chip IC5, the suffix “a” is added to the numeral or symbolof the structure in the semiconductor chip IC5. In addition, in thesemiconductor chip IC5 a, description of the structure described in thesemiconductor chip IC5 is appropriately omitted. Note that the“comparing circuit CNa” is referred to as the “comparing circuit CNaaa”here, in order to discriminate from the “comparing circuit CNaa”illustrated in FIG. 13 or the like.

The semiconductor chip IC5 a has electrode pads for external electricconnection, which include the electrode pad T1 a, the electrode pad T2a, the electrode pad T3 a, the electrode pad T4 a, and the electrode padT5 a. In addition, the semiconductor chip IC5 a includes a lightemission control unit HC5 a as the second light emission control unit,the dimming circuit LC1 a, and the dimming circuit LC2 a as the seconddimming portion. The light emission control unit HC5 a includes acomparing circuit CNaaa as the second comparing circuit, a transistor N3a, a transistor N4 a as the second control switch, and a transistor P12a.

The dimming circuit LC11 has one terminal connected to the electrode padT1 a, i.e. connected to the power supply circuit VS via the electrodepad T1 a, and the other terminal connected to the electrode pad T2 a.

The dimming circuit LC12 has one terminal connected to the electrode padT1 a, i.e. connected to the power supply circuit VS via the electrodepad T1 a, and the other terminal connected to the electrode pad T3 a.

The electrode pad T4 a is connected to the power supply circuit VS. Inthis way, in the transistor P12 a, the gate terminal G is alwaysconnected to the power supply circuit VS. Therefore, the transistor P12a is not turned on even if the voltage level of the drive voltage Vk isincreased, and is always in off state.

The electrode pad T5 a is connected to the electrode pad T5 of thesemiconductor chip IC5 via the wiring W3. In other words, the wiring W3electrically connects the node Nd14 and a node Nd14 a. In this way, thegate terminals G of the transistor N3 and the transistor N4 areelectrically connected to the gate terminals G of the transistor N3 aand the transistor N4 a.

As described above, in the lighting device 40 h, the gate terminal G ofthe transistor P12 of the semiconductor chip IC5 is electricallyconnected to the power supply VSS in the light emission control unitHC5, and hence supply of the comparison result signal Vcr2 from thecomparing circuit CNa to the gate terminals G of the transistor N3 andthe transistor N4 is performed. In addition, in the light emissioncontrol unit HC5 a, the gate terminals G of the transistor N3 a and thetransistor N4 a of the semiconductor chip IC5 a are electricallyconnected to the power supply circuit VS, and hence supply of thecomparison result signal Vcr2 a from the comparing circuit CNaaa to thegate terminals G of the transistor N3 a and the transistor N4 a isinterrupted. In addition, the gate terminals G of the transistor N3 andthe transistor N4 connected to the comparing circuit CNa areelectrically connected to the gate terminals G of the transistor N3 aand the transistor N4 a via the wiring W3. Further, in this way, in thelighting device 40 h, the light emission control unit HC5 of thesemiconductor chip IC5 performs the light emission control and the lightemission stop control of the light emitting element groups HS connectedto the semiconductor chip IC5 and the light emission control and thelight emission stop control of the light emitting element groups HSaconnected to the semiconductor chip IC5 a, i.e. performs the lightemission control and the light emission stop control of the lightemitting element groups HSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CNa of the semiconductor chip IC5 and the comparingcircuit CNaaa of the semiconductor chip IC5 a, the lighting device 40 hcan prevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

In addition, as to the lighting device 40 h, in the case where thewiring resistance of the wiring W1 for the semiconductor chip IC5 toreceive power supply of the drive voltage Vk and the drive current Ikfrom the power supply circuit VS is larger than the wiring resistance ofthe wiring W2 for the semiconductor chip IC5 a to receive power supplyof the drive voltage Vk and the drive current Ik from the power supplycircuit VS, the light emission control unit HC5 of the semiconductorchip IC5 performs the light emission control and the light emission stopcontrol of the light emitting element groups HS connected to thesemiconductor chip IC5, and performs the light emission control and thelight emission stop control of the light emitting element groups HSaconnected to the semiconductor chip IC5 a. Therefore, even if apotential increase in the drive voltage Vk obtained by the comparingcircuit CNa of the semiconductor chip IC5 is delayed from a potentialincrease in the drive voltage Vk obtained by the comparing circuit CNaaaof the semiconductor chip IC5 a, based on the wiring resistancedifference between the wiring W1 and the wiring W2, it is possible toprevent a light emission timing variation between the light emittingelement groups HS and the light emitting element groups HSa.

Ninth Variation of Fourth Embodiment

FIG. 22 is a diagram illustrating a lighting device 40 i according to aninth variation of the fourth embodiment of the present invention. Thelighting device 40 i includes the power supply circuit VS, the lightemitting element groups HSB, the semiconductor chip IC5, and thesemiconductor chip IC5 a. Note that in the lighting device 40 iillustrated in FIG. 22, the same structure as in the lighting device 40h illustrated in FIG. 21 is denoted by the same numeral or symbol, anddescription thereof is appropriately omitted.

The lighting device 40 i is substantially different from the lightingdevice 40 h in the connection destination of the electrode pad T4 of thesemiconductor chip IC5 and in the connection destination of theelectrode pad T4 a of the semiconductor chip IC5 a.

The electrode pad T4 is connected to the power supply circuit VS. Inthis way, in the transistor P12, the gate terminal G is always connectedto the power supply circuit VS. Therefore, the transistor P12 is notturned on even if the voltage level of the drive voltage Vk isincreased, and is always in off state.

In addition, the electrode pad T4 a is connected to the power supplyVSS. In this way, in the transistor P12 a, the gate terminal G isconnected to the power supply VSS. Therefore, the transistor P12 a isturned on when the drive voltage Vk is increased so that the gate-sourcevoltage of the transistor P12 becomes equal to or higher than athreshold voltage.

As described above, in the lighting device 40 i, the gate terminal G ofthe transistor P12 of the semiconductor chip IC5 is electricallyconnected to the power supply circuit VS in the light emission controlunit HC5, and hence supply of the comparison result signal Vcr2 from thecomparing circuit CNa to the gate terminals G of the transistor N3 andthe transistor N4 is interrupted. In addition, in the light emissioncontrol unit HC5 a, the gate terminal G of the transistor P12 a of thesemiconductor chip IC5 a is electrically connected to the power supplyVSS, and hence supply of the comparison result signal Vcr2 a from thecomparing circuit CNaaa to the gate terminals G of the transistor N3 aand the transistor N4 a is performed. In addition, the gate terminals Gof the transistor N3 a and the transistor N4 a connected to thecomparing circuit CNaaa are electrically connected to the gate terminalsG of the transistor N3 and the transistor N4 via the wiring W3. Further,in this way, in the lighting device 40 i, the light emission controlunit HC5 a of the semiconductor chip IC5 a performs the light emissioncontrol and the light emission stop control of the light emittingelement groups HS connected to the semiconductor chip IC5, and the lightemission control and the light emission stop control of the lightemitting element groups HSa connected to the semiconductor chip IC5 a,i.e. performs the light emission control and the light emission stopcontrol of the light emitting element groups HSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CNa of the semiconductor chip IC5 and the comparingcircuit CNaaa of the semiconductor chip IC5 a, the lighting device 40 ican prevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

Note that the light emission control and the light emission stop controlof the lighting device including the semiconductor chip IC5 and thesemiconductor chip IC5 a are performed by either one of the lightemission control unit HC5 of the semiconductor chip IC5 and the lightemission control unit HC5 a of the semiconductor chip IC5 a, asdescribed above.

Tenth Variation of Fourth Embodiment

FIG. 23 is a diagram illustrating a lighting device 40 j according to atenth variation of the fourth embodiment of the present invention. Thelighting device 40 j includes the power supply circuit VS, the lightemitting element groups HSB, a semiconductor chip IC6 as the firstsemiconductor chip, and a semiconductor chip IC6 a as the secondsemiconductor chip. Note that in the lighting device 40 j illustrated inFIG. 23, the same structure as in the lighting device 30 c illustratedin FIG. 12, or the lighting device 40 illustrated in FIG. 13 is denotedby the same numeral or symbol, and description thereof is appropriatelyomitted.

The semiconductor chip IC6 has electrode pads for external electricconnection, which include the electrode pad T1, the electrode pad T2,the electrode pad T3, the electrode pad T4, the electrode pad T5, theelectrode pad T6, and the electrode pad T7. In addition, thesemiconductor chip IC4 includes the light emission control unit HC4 asthe first light emission control unit, the dimming circuit LC11, and thedimming circuit LC12 as the first dimming portion.

A light emission control unit HC6 includes the comparing circuit CN asthe first comparing circuit, and a transistor P13 as the third controlswitch.

The comparing circuit CN is connected to the electrode pad T1, i.e. isconnected to the power supply circuit VS via the electrode pad T1. Thecomparing circuit CN determines whether the drive voltage Vk is higheror lower than the light emission reference voltage VH or a voltage basedon the light emission reference voltage VH, and outputs a result of thecomparison as the comparison result signal Vcr1.

The dimming circuit LC11 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1, and the other terminal connected to the electrode pad T2, i.e.connected to one terminal of the light emitting element group HS1 viathe electrode pad T2, and connected to the electrode pad T6, i.e.connected to the node Nd8 of the light emitting element group HS1 viathe electrode pad T6. Note that the dimming circuit LC11 includes thedriving circuit KD1 illustrated in FIG. 12.

The dimming circuit LC12 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1, and the other terminal connected to the electrode pad T3, i.e.connected to the one terminal of the light emitting element group HS2via the electrode pad T3, and connected to the electrode pad T7, i.e.connected to the node Nd9 of the light emitting element group HS2 viathe electrode pad T7. Note that the dimming circuit LC12 includes thedriving circuit KD2 illustrated in FIG. 12.

The transistor P13 is a PMOS transistor, which has the source terminal Sconnected to the comparing circuit CN, and the drain terminal Dconnected to the driving circuit KD1 of the dimming circuit LC11 and thedriving circuit KD2 of the dimming circuit 12. In this way, thecomparing circuit CN is connected to the driving circuit KD1 via thetransistor P13, while the comparing circuit CN is connected to thedriving circuit KD2 via the transistor P13. The electric connectionbetween the comparing circuit CN and the driving circuit KD1, and theelectric connection between the comparing circuit CN and the drivingcircuit KD2 are controlled by the transistor P13. In addition, thetransistor P13 has the gate terminal G connected to the electrode padT4, i.e. connected to the power supply VSS via the electrode pad T4. Inthis way, the transistor P13 is turned on when the drive voltage Vk isincreased, and the signal level of the comparison result signal Vcr1,which is output from the comparing circuit CN and is supplied to thesource terminal S of the transistor P13, is increased so that thegate-source voltage of the transistor P13 becomes equal to or higherthan a threshold voltage. Here, the connection node among the drainterminal D of the transistor P13, the driving circuit KD1, and thedriving circuit KD2 is referred to as a node Nd15.

The semiconductor chip IC6 a has the same structure as the semiconductorchip IC6. However, in the semiconductor chip IC6 a of FIG. 23, forconvenience of description, in order to discriminate from thesemiconductor chip IC6, the suffix “a” is added to the numeral or symbolof the structure in the semiconductor chip IC6. In addition, in thesemiconductor chip IC6 a, description of the structure described in thesemiconductor chip IC6 is appropriately omitted. Note that the“comparing circuit CN” is referred to as the “comparing circuit CNaa”here, in order to discriminate from the “comparing circuit CNa”illustrated in FIG. 13 or the like.

The semiconductor chip IC6 a has electrode pads for external electricconnection, which include the electrode pad T1 a, the electrode pad T2a, the electrode pad T3 a, the electrode pad T4 a, the electrode pad T5a, the electrode pad T6 a, and the electrode pad T7 a. In addition, thesemiconductor chip IC6 a includes a light emission control unit HC6 a asthe second light emission control unit, a dimming circuit LC11 a, and adimming circuit LC12 a as the second dimming portion. The light emissioncontrol unit HC6 a includes the comparing circuit CNaa as the secondcomparing circuit, and a transistor P13 a.

The dimming circuit LC11 a has one terminal connected to the electrodepad T1 a, i.e. connected to the power supply circuit VS via theelectrode pad T1 a, and the other terminal connected to the electrodepad T2 a, i.e. connected to the one terminal of the light emittingelement group HS11 via the electrode pad T2 a, and connected to theelectrode pad T6 a, i.e. connected to a node Nd8 a of the light emittingelement group HS11 via the electrode pad T6 a.

The dimming circuit LC12 a has one terminal connected to the electrodepad T1 a, i.e. connected to the power supply circuit VS via theelectrode pad T1 a, and the other terminal connected to the electrodepad T3 a, i.e. connected to the one terminal of the light emittingelement group HS12 via the electrode pad T3 a, and connected to theelectrode pad T7 a, i.e. connected to a node Nd9 a of the light emittingelement group HS12 via the electrode pad T7 a.

The electrode pad T4 a is connected to the power supply circuit VS. Inthis way, in the transistor P13 a, the gate terminal G is alwaysconnected to the power supply circuit VS. Therefore, the transistor P13a is not turned on even if the voltage level of the drive voltage Vk isincreased, and is always in off state.

The electrode pad T5 a is connected to the electrode pad T5 of thesemiconductor chip IC6 via the wiring W3. In other words, the wiring W3electrically connects the node Nd15 and the node Nd15 a. In this way,the driving circuit KD1 and the driving circuit KD2 are electricallyconnected to a driving circuit KD1 a and a driving circuit KD2 a.

As described above, in the lighting device 40 j, the gate terminal G ofthe transistor P13 of the semiconductor chip IC6 is electricallyconnected to the power supply VSS in the light emission control unitHC6, and hence supply of the comparison result signal Vcr1 from thecomparing circuit CN to the driving circuit KD1 and the driving circuitKD2 is performed. In addition, the gate terminal G of the transistor P13a of the semiconductor chip IC6 a is electrically connected to the powersupply circuit VS in the light emission control unit HC6 a, and hencesupply of the comparison result signal Vcr1 a from the comparing circuitCNaa to the driving circuit KD1 and the driving circuit KD2 isinterrupted. In addition, the driving circuit KD1 and the drivingcircuit KD2 connected to the comparing circuit CN are electricallyconnected to the driving circuit KD1 a and the driving circuit KD2 a viathe wiring W3. Further, in this way, in the lighting device 40 j, thelight emission control unit HC6 of the semiconductor chip IC6 performsthe light emission control and the light emission stop control of thelight emitting element groups HS connected to the semiconductor chipIC6, and the light emission control and the light emission stop controlof the light emitting element groups HSa connected to the semiconductorchip IC6 a, i.e. performs the light emission control and the lightemission stop control of the light emitting element groups HSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CN of the semiconductor chip IC6 and the comparingcircuit CNaa of the semiconductor chip IC6 a, the lighting device 40 jcan prevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

In addition, in the lighting device 40 j, in the case where the wiringresistance of the wiring W1 for the semiconductor chip IC6 to receivepower supply of the drive voltage Vk and the drive current Ik from thepower supply circuit VS is larger than the wiring resistance of thewiring W2 for the semiconductor chip IC6 a to receive power supply ofthe drive voltage Vk and the drive current Ik from the power supplycircuit VS, the light emission control and the light emission stopcontrol of the light emitting element groups HS connected to thesemiconductor chip IC6, and the light emission control and the lightemission stop control of the light emitting element groups HSa connectedto the semiconductor chip IC6 a are performed by the light emissioncontrol unit HC6 of the semiconductor chip IC6. Therefore, even if apotential increase in the drive voltage Vk obtained by the comparingcircuit CNa of the semiconductor chip IC6 is delayed from a potentialincrease in the drive voltage Vk obtained by the comparing circuit CNaaaof the semiconductor chip IC6 a, based on the wiring resistancedifference between the wiring W1 and the wiring W2, it is possible toprevent a light emission timing variation between the light emittingelement groups HS and the light emitting element groups HSa.

Eleventh Variation of Fourth Embodiment

FIG. 24 is a diagram illustrating a lighting device 40 k according to aneleventh variation of the fourth embodiment of the present invention.The lighting device 40 k includes the power supply circuit VS, the lightemitting element groups HSB, the semiconductor chip IC6, and thesemiconductor chip IC6 a. Note that in the lighting device 40 killustrated in FIG. 24, the same structure as in the lighting device 40j illustrated in FIG. 23 is denoted by the same numeral or symbol, anddescription thereof is appropriately omitted.

The lighting device 40 k is substantially different from the lightingdevice 40 j in the connection destination of the electrode pad T4 of thesemiconductor chip IC6 and in the connection destination of theelectrode pad T4 a of the semiconductor chip IC6 a.

The electrode pad T4 is connected to the power supply circuit VS. Inthis way, in the transistor P13, the gate terminal G is always connectedto the power supply circuit VS. Therefore, the transistor P13 is notturned on even if the voltage level of the drive voltage Vk isincreased, and is always in off state.

In addition, the electrode pad T4 a is connected to the power supplyVSS. In this way, in the transistor P13 a, the gate terminal G isconnected to the power supply VSS. Therefore, the transistor P13 a isturned on when the drive voltage Vk is increased so that the gate-sourcevoltage of the transistor P13 becomes equal to or higher than athreshold voltage.

As described above, in the lighting device 40 k, the gate terminal G ofthe transistor P13 of the semiconductor chip IC6 is electricallyconnected to the power supply circuit VS in the light emission controlunit HC6, and hence supply of the comparison result signal Vcr1 from thecomparing circuit CN to the driving circuit KD1 and the driving circuitKD2 is interrupted. In addition, in the light emission control unit HC6a, the gate terminal G of the transistor P13 a of the semiconductor chipIC6 a is electrically connected to the power supply VSS, and hencesupply of the comparison result signal Vcr1 a from the comparing circuitCNaa to the gate terminals G of the driving circuit KD1 a and thedriving circuit KD2 a is performed. In addition, the driving circuit KD1a and the driving circuit KD2 a connected to the comparing circuit CNaaare electrically connected to the driving circuit KD1 and the drivingcircuit KD2 via the wiring W3. Further, in this way, in the lightingdevice 40 k, the light emission control unit HC6 a of the semiconductorchip IC6 a performs the light emission control and the light emissionstop control of the light emitting element groups HS connected to thesemiconductor chip IC6, and the light emission control and the lightemission stop control of the light emitting element groups HSa connectedto the semiconductor chip IC6 a, i.e. performs the light emissioncontrol and the light emission stop control of the light emittingelement groups HSB.

Therefore, even if there is a manufacturing variation between thecomparing circuit CN of the semiconductor chip IC6 and the comparingcircuit CNaa of the semiconductor chip IC6 a, the lighting device 40 kcan prevent a variation in timing of causing as well as stopping lightemission of the light emitting element groups HS and the light emittingelement groups HSa.

Fifth Embodiment

FIG. 25 is a diagram illustrating a lighting device 50 according to afifth embodiment of the present invention. The lighting device 50includes the power supply circuit VS, the light emitting element groupsHSB, a semiconductor chip IC7 as the first semiconductor chip, and asemiconductor chip IC7 a as the second semiconductor chip. Note that inthe lighting device 50 illustrated in FIG. 25, the same structure as inthe lighting device 10 illustrated in FIG. 1, the lighting device 10 aillustrated in FIG. 3, or the lighting device 40 illustrated in FIG. 13is denoted by the same numeral or symbol, and description thereof isappropriately omitted.

The light emitting element groups HSB include the light emitting elementgroups HS and the light emitting element groups HSa. The light emittingelement groups HS include the light emitting element group HS1, and thelight emitting element group HS2 as the first light emitting elementgroup. The light emitting element groups HSa include the light emittingelement group HS11 and the light emitting element group HS12 as thesecond light emitting element group.

The semiconductor chip IC7 has electrode pads for external electricconnection, which include the electrode pad T1, the electrode pad T2,the electrode pad T3, the electrode pad T8, and the electrode pad T9. Inaddition, the semiconductor chip IC7 includes a light emission controlunit HC7 as the first light emission control unit, the dimming circuitLC1, and the dimming circuit LC2 as the first dimming portion.

The electrode pad T1 is connected to the power supply circuit VS via thewiring W1 as the first power supply wiring. In other words, the wiringW1 is connected to the power supply circuit VS and the semiconductorchip IC7. The electrode pad T2 is connected to the node Nh1 of the lightemitting element group HS1. The electrode pad T3 is connected to thenode Nh2 of the light emitting element group HS2.

The light emission control unit HC7 includes the comparing circuit CN asthe first comparing circuit, the detecting portion K1 as the firstdetecting portion, and the transistor P1 as the first control switch.

The comparing circuit CN is connected to the electrode pad T1, i.e. isconnected to the power supply circuit VS via the electrode pad T1. Thecomparing circuit CN determines whether the drive voltage Vk is higheror lower than the light emission reference voltage VHa or a voltagebased on the light emission reference voltage VHa, and outputs a resultof the comparison as the comparison result signal Vcr1. Note that theoutput terminal of the comparing circuit CN is connected to theelectrode pad T8.

The detecting portion K1 is an OR circuit having a first input terminaland a second input terminal, for example. The first input terminal ofthe detecting portion K1 is connected to the output terminal of thecomparing circuit CN and is supplied with the comparison result signalVcr1. In addition, the first input terminal of the detecting portion K1is connected to the electrode pad T8, and the second input terminal isconnected to the electrode pad T9. The detecting portion K1 outputs anoutput signal Ko1, which is the logical sum of the signal input to thefirst input terminal and the signal input to the second input terminal.Here, the connection node between the first input terminal of thedetecting portion K1 and the comparing circuit CN is referred to as anode Nd16. Note that the detecting portion K1 is not limited to the ORcircuit but may be any other logic circuit, as long as it outputs theoutput signal Ko1 as a result, which is the logical sum of the signalinput to the first input terminal and the signal input to the secondinput terminal.

The transistor P1 is a PMOS transistor, which has the source terminal Sconnected to the electrode pad T1, i.e. connected to the power supplycircuit VS via the electrode pad T1, and the gate terminal G connectedto the output terminal of the detecting portion K1. The transistor P1 ison-off controlled by the output signal Ko1 supplied from the detectingportion K1.

The dimming circuit LC1 has one terminal connected to the drain terminalD of the transistor P1 of the light emission control unit HC7. Inaddition, the dimming circuit LC1 has the other terminal connected tothe electrode pad T2, i.e. connected to the node Nh1 of the lightemitting element group HS1 via the electrode pad T2.

The dimming circuit LC2 has one terminal connected to the drain terminalD of the transistor P1 of the light emission control unit HC7. Inaddition, the dimming circuit LC2 has the other terminal connected tothe electrode pad T3, i.e. connected to the node Nh2 of the lightemitting element group HS2 via the electrode pad T3.

The semiconductor chip IC7 a has the same structure as the semiconductorchip IC7. However, in the semiconductor chip IC7 a of FIG. 25, forconvenience of description, in order to discriminate from thesemiconductor chip IC7, the suffix “a” is added to the numeral or symbolof the structure in the semiconductor chip IC7. In addition, in thesemiconductor chip IC7 a, description of the structure described in thesemiconductor chip IC7 is appropriately omitted. Note that the“comparing circuit CN” is referred to as a “comparing circuit CNaa”here, in order to discriminate from the “comparing circuit CNa”illustrated in FIG. 5 or the like.

The semiconductor chip IC7 a has electrode pads for external electricconnection, which include the electrode pad T1 a, the electrode pad T2a, the electrode pad T3 a, the electrode pad T8 a, and the electrode padT9 a. In addition, the semiconductor chip IC7 a includes a lightemission control unit HC7 a as the second light emission control unit,the dimming circuit LC1 a, and the dimming circuit LC2 a as the seconddimming portion.

The electrode pad T1 a is connected to the power supply circuit VS viathe wiring W2 as the second power supply wiring. In other words, thewiring W2 is connected to the power supply circuit VS and thesemiconductor chip IC7 a. The electrode pad T2 a is connected to thenode Nh11 of the light emitting element group HS11. The electrode pad T3a is connected to the node Nh12 of the light emitting element groupHS12. Note that the wiring resistance of the wiring W2 may be differentfrom the wiring resistance of the wiring W1.

The light emission control unit HC7 a includes the comparing circuit CNaas the second comparing circuit, a detecting portion K1 a as the seconddetecting portion, and the transistor P1 a as the second control switch.

The dimming circuit LC1 a has one terminal connected to the drainterminal D of the transistor P1 a of the light emission control unit HC7a. In addition, the dimming circuit LC1 a has the other terminalconnected to the electrode pad T2 a, i.e. connected to the node Nh11 ofthe light emitting element group HS11 via the electrode pad T2 a.

The dimming circuit LC2 a has one terminal connected to the drainterminal D of the transistor P1 a of the light emission control unit HC7a. In addition, the dimming circuit LC2 a has the other terminalconnected to the electrode pad T3 a, i.e. connected to the node Nh12 ofthe light emitting element group HS12 via the electrode pad T3 a.

The electrode pad T8 a is connected to the electrode pad T9 of thesemiconductor chip IC7 via the wiring W4 as the second connectionwiring. In other words, the wiring W4 electrically connects a node Nd16a and the second input terminal of the detecting portion K1.

The electrode pad T9 a is connected to the electrode pad T8 of thesemiconductor chip IC7 via the wiring W5 as the third connection wiring.In other words, the wiring W5 electrically connects the node Nd16 andthe second input terminal of the detecting portion K1 a.

Here, in the detecting portion K1 of the semiconductor chip IC7, thefirst input terminal is supplied with the comparison result signal Vcr1output from the comparing circuit CN, the second input terminal issupplied with the comparison result signal Vcr1 a output from thecomparing circuit CNaa of the semiconductor chip IC7 a, and the logicalsum of these signals is supplied to the gate terminal G of thetransistor P1 as the output signal Ko1 as the first output signal, andthus the transistor P1 is on-off controlled. In other words, the lightemission control and the light emission stop control of the lightemitting element groups HS are performed by the light emission controlunit HC7 and the light emission control unit HC7 a of the semiconductorchip IC7 a.

In addition, in the detecting portion K1 a of the semiconductor chip IC7a, the first input terminal is supplied with the comparison resultsignal Vcr1 output from the comparing circuit CN of the semiconductorchip IC7, the second input terminal is supplied with the comparisonresult signal Vcr1 a output from the comparing circuit CNaa, and thelogical sum of these signals is supplied to the gate terminal G of thetransistor P1 a as the output signal Ko1 a as the second output signal,and thus the transistor P1 a is on-off controlled. In other words, thelight emission control and the light emission stop control of the lightemitting element groups HSa is performed by the light emission controlunit HC7 a and the light emission control unit HC7 of the semiconductorchip IC7.

Here, the on/off state of the transistor P1 is determined by the signallevel of the output signal Ko1 of the detecting portion K1 and thesignal level of the output signal Ko1 a of the detecting portion K1 a.Further, the signal level of the output signal Ko1 of the detectingportion K1 and the signal level of the output signal Ko1 a of thedetecting portion K1 a are determined by the level of the comparisonresult signal Vcr1 output from the comparing circuit CN and the level ofthe comparison result signal Vcr1 a output from the comparing circuitCNaa.

If each of the comparing circuit CN and the comparing circuit CNaadetermines that the drive voltage Vk is lower than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr1 and the comparison resultsignal Vcr1 a become high level. Therefore, high level signals are inputto the first input terminal and the second input terminal of each of thedetecting portion K1 and the detecting portion K1 a, and the outputsignal Ko1 and the output signal Ko1 a become high level. In this case,the gate terminals G of the transistor P1 and the transistor P1 a aresupplied with the high level signal, and hence the transistor P1 and thetransistor P1 a are both turned off.

If the comparing circuit CN determines that the drive voltage Vk islower than the light emission reference voltage VHa or a voltage basedon the light emission reference voltage VHa, while the comparing circuitCNaa determines that the drive voltage Vk is higher than the lightemission reference voltage VHa or a voltage based on the light emissionreference voltage VHa, the comparison result signal Vcr1 becomes highlevel, while the comparison result signal Vcr1 a becomes low level. Inthis case, the second input terminal of the detecting portion K1 and thefirst input terminal of the detecting portion K1 a are supplied with thelow level signal, while the first input terminal of the detectingportion K1 and the second input terminal of the detecting portion K1 aare supplied with the high level signal. Therefore, the output signalKo1 and the output signal Ko1 a become high level. In this case, thegate terminals G of the transistor P1 and the transistor P1 a aresupplied with the high level signal, and hence the transistor P1 and thetransistor P1 a are both turned off.

If each of the comparing circuit CN and the comparing circuit CNaadetermines that the drive voltage Vk is higher than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr1 and the comparison resultsignal Vcr1 a become low level. Therefore, the first input terminal andthe second input terminal of each of the detecting portion K1 and thedetecting portion K1 a are supplied with the low level signal, and hencethe output signal Ko1 and the output signal Ko1 a become low level. Inthis case, the gate terminals G of the transistor P1 and the transistorP1 a are supplied with the low level signal, and hence the transistor P1and the transistor P1 a are both turned on.

As described above, in the lighting device 50, the light emissioncontrol and the light emission stop control of the light emittingelement groups HSB are performed by the light emission control unit HC7of the semiconductor chip IC7 and the light emission control unit HC7 aof the semiconductor chip IC7 a. Therefore, even if there is amanufacturing variation between the comparing circuit CN of thesemiconductor chip IC7 and the comparing circuit CNaa of thesemiconductor chip IC7 a, the lighting device 50 can prevent a variationin timing of causing as well as stopping light emission of the lightemitting element groups HS and the light emitting element groups HSa.

In addition, in the lighting device 50, the light emission control andthe light emission stop control of the light emitting element groups HSBare performed by the light emission control unit HC7 of thesemiconductor chip IC7 and the light emission control unit HC7 a of thesemiconductor chip IC7 a. Therefore, even if the wiring resistance ofthe wiring W2 for the semiconductor chip IC7 a to receive power supplyof the drive voltage Vk and the drive current Ik from the power supplycircuit VS is different from the wiring resistance of the wiring W1 forthe semiconductor chip IC7 to receive power supply of the drive voltageVk and the drive current Ik from the power supply circuit VS, thelighting device 50 can prevent a variation in timing of causing as wellas stopping light emission of the light emitting element groups HS andthe light emitting element groups HSa.

First Variation of Fifth Embodiment

FIG. 26 is a diagram illustrating a lighting device 50 a according to afirst variation of the fifth embodiment of the present invention. Thelighting device 50 a includes the power supply circuit VS, the lightemitting element groups HSB, a semiconductor chip IC8 as the firstsemiconductor chip, and a semiconductor chip IC8 a as the secondsemiconductor chip. Note that in the lighting device 50 a illustrated inFIG. 26, the same structure as in the lighting device 10 b illustratedin FIG. 4 or the lighting device 40 b illustrated in FIG. 15 is denotedby the same numeral or symbol, and description thereof is appropriatelyomitted.

The light emitting element groups HSB include the light emitting elementgroups HS and the light emitting element groups HSa. The light emittingelement groups HS include the light emitting element group HS1, and thelight emitting element group HS2 as the first light emitting elementgroup. The light emitting element groups HSa include the light emittingelement group HS11, and the light emitting element group HS12 as thesecond light emitting element group.

The semiconductor chip IC8 has electrode pads for external electricconnection, which include the electrode pad T1, the electrode pad T2,the electrode pad T3, the electrode pad T8, and the electrode pad T9. Inaddition, the semiconductor chip IC8 includes the light emission controlunit HC7 as the first light emission control unit, the dimming circuitLC1, and the dimming circuit LC2 as the first dimming portion.

The electrode pad T1 is connected to the power supply circuit VS via thewiring W1 as the first power supply wiring. In other words, the wiringW1 is connected to the power supply circuit VS and the semiconductorchip IC8. The electrode pad T2 is connected to the node Nh1 of the lightemitting element group HS1. The electrode pad T3 is connected to thenode Nh2 of the light emitting element group HS2.

A light emission control unit HC8 includes the comparing circuit CN asthe first comparing circuit, the detecting portion K1 as the firstdetecting portion, the transistor P2, and the transistor P3 as the firstcontrol switch.

The dimming circuit LC1 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1.

The dimming circuit LC2 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1.

The transistor P2 is a PMOS transistor, which has the source terminal Sconnected to the other terminal of the dimming circuit LC1 and the drainterminal D connected to the electrode pad T2, i.e. connected to the nodeNh1 of the light emitting element group HS1 via the electrode pad T2. Inaddition, the transistor P2 has the gate terminal G connected to theoutput terminal of the detecting portion K1. The transistor P2 is on-offcontrolled by the output signal Ko1 supplied from the detecting portionK1.

The transistor P3 is a PMOS transistor, which has the source terminal Sconnected to the other terminal of the dimming circuit LC2 and the drainterminal D connected to the electrode pad T3, i.e. connected to the nodeNh2 of the light emitting element group HS2 via the electrode pad T3. Inaddition, the transistor P3 has the gate terminal G connected to theoutput terminal of the detecting portion K1. The transistor P3 is on-offcontrolled by the output signal Ko1 supplied from the detecting portionK1.

The semiconductor chip IC8 a has the same structure as the semiconductorchip IC8. However, in the semiconductor chip IC8 a of FIG. 26, forconvenience of description, in order to discriminate from thesemiconductor chip IC8, the suffix “a” is added to the numeral or symbolof the structure in the semiconductor chip IC8. In addition, in thesemiconductor chip IC8 a, description of the structure described in thesemiconductor chip IC8 is appropriately omitted. Note that the“comparing circuit CN” is referred to as a “comparing circuit CNaa”here, in order to discriminate from the “comparing circuit CNa”illustrated in FIG. 5 or the like.

The semiconductor chip IC8 a has electrode pads for external electricconnection, which include the electrode pad T1 a, the electrode pad T2a, the electrode pad T3 a, the electrode pad T8 a, and the electrode padT9 a. In addition, the semiconductor chip IC8 a includes a lightemission control unit HC8 a as the second light emission control unit,the dimming circuit LC1 a, and the dimming circuit LC2 a as the seconddimming portion. The light emission control unit HC8 a includes thecomparing circuit CNaa as the second comparing circuit, the detectingportion K1 a as the second detecting portion, the transistor P2 a, andthe transistor P3 a as the second control switch.

The electrode pad T1 a is connected to the power supply circuit VS viathe wiring W2 as the second power supply wiring. In other words, thewiring W2 is connected to the power supply circuit VS and thesemiconductor chip IC8 a. The electrode pad T2 a is connected to thenode Nh11 of the light emitting element group HS11. The electrode pad T3a is connected to the node Nh12 of the light emitting element groupHS12. Note that the wiring resistance of the wiring W2 may be differentfrom the wiring resistance of the wiring W1.

The dimming circuit LC1 a has one terminal connected to the electrodepad T1 a, i.e. connected to the power supply circuit VS via theelectrode pad T1 a.

The dimming circuit LC2 a has one terminal connected to the electrodepad T1 a, i.e. connected to the power supply circuit VS via theelectrode pad T1 a.

The electrode pad T8 a is connected to the electrode pad T9 of thesemiconductor chip IC8 via the wiring W4 as the second connectionwiring. In other words, the wiring W4 electrically connects the nodeNd16 a and the second input terminal of the detecting portion K1.

The electrode pad T9 a is connected to the electrode pad T8 of thesemiconductor chip IC8 via the wiring W5 as the third connection wiring.In other words, the wiring W5 electrically connects the node Nd16 andthe second input terminal of the detecting portion K1 a.

Here, in the detecting portion K1 of the semiconductor chip IC8, thefirst input terminal is supplied with the comparison result signal Vcr1output from the comparing circuit CN, the second input terminal issupplied with the comparison result signal Vcr1 a output from thecomparing circuit CNaa of the semiconductor chip IC8 a, and the logicalsum of these signals is supplied to the gate terminals G of thetransistor P2 and the transistor P3 as the output signal Ko1 as thefirst output signal so that the transistor P2 and the transistor P3 areon-off controlled. In other words, the light emission control and thelight emission stop control of the light emitting element groups HS areperformed by the light emission control unit HC8 and the light emissioncontrol unit HC8 a of the semiconductor chip IC8 a.

In addition, in the detecting portion K1 a of the semiconductor chip IC8a, the first input terminal is supplied with the comparison resultsignal Vcr1 output from the comparing circuit CN of the semiconductorchip IC8, the second input terminal is supplied with the comparisonresult signal Vcr1 a output from the comparing circuit CNaa, and thelogical sum of these signals is supplied to the gate terminals G of thetransistor P2 a and the transistor P3 a as the output signal Ko1 a asthe second output signal so that the transistor P2 a and the transistorP3 a are on-off controlled. In other words, the light emission controland the light emission stop control of the light emitting element groupsHSa are performed by the light emission control unit HC8 a and the lightemission control unit HC8 of the semiconductor chip IC8.

Here, the on/off states of the transistor P2 and the transistor P3 aredetermined by the signal level of the output signal Ko1 of the detectingportion K1 and the signal level of the output signal Ko1 a of thedetecting portion K1 a. Further, the signal level of the output signalKo1 of the detecting portion K1 and the signal level of the outputsignal Ko1 a of the detecting portion K1 a are determined by the levelof the comparison result signal Vcr1 output from the comparing circuitCN and the level of the comparison result signal Vcr1 a output from thecomparing circuit CNaa.

If each of the comparing circuit CN and the comparing circuit CNaadetermines that the drive voltage Vk is lower than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr1 and the comparison resultsignal Vcr1 a become high level. Therefore, the first input terminal andthe second input terminal of each of the detecting portion K1 and thedetecting portion K1 a are supplied with the high level signal, andhence the output signal Ko1 and the output signal Ko1 a become highlevel. In this case, the transistor P2, the transistor P3, the gateterminals G of the transistor P2 a and the transistor P3 a are suppliedwith the high level signal, and hence the transistor P2, the transistorP3, the transistor P2 a, and the transistor P3 a are all turned off.

If the comparing circuit CN determines that the drive voltage Vk islower than the light emission reference voltage VHa or a voltage basedon the light emission reference voltage VHa, while the comparing circuitCNaa determines that the drive voltage Vk is higher than the lightemission reference voltage VHa or a voltage based on the light emissionreference voltage VHa, the comparison result signal Vcr1 becomes highlevel, while the comparison result signal Vcr1 a becomes low level. Inthis case, the second input terminal of the detecting portion K1 and thefirst input terminal of the detecting portion K1 a are supplied with thelow level signal, and the first input terminal of the detecting portionK1 and the second input terminal of the detecting portion K1 a aresupplied with the high level signal. Therefore, the output signal Ko1and the output signal Ko1 a become high level. In this case, thetransistor P2, the transistor P3, the gate terminals G of the transistorP2 a and the transistor P3 a are supplied with the high level signal,and hence the transistor P2, the transistor P3, the transistor P2 a andthe transistor P3 a are all turned off.

If each of the comparing circuit CN and the comparing circuit CNaadetermines that the drive voltage Vk is higher than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr1 and the comparison resultsignal Vcr1 a become low level. Therefore, the first input terminal andthe second input terminal of each of the detecting portion K1 and thedetecting portion K1 a are supplied with the low level signal, and hencethe output signal Ko1 and the output signal Ko1 a become low level. Inthis case, the transistor P2, the transistor P3, the gate terminals G ofthe transistor P2 a and the transistor P3 a are supplied with the lowlevel signal, and hence the transistor P2, the transistor P3, thetransistor P2 a, and the transistor P3 a are all turned on.

As described above, in the lighting device 50 a, the light emissioncontrol and the light emission stop control of the light emittingelement groups HSB are performed by the light emission control unit HC8of the semiconductor chip IC8 and the light emission control unit HC8 aof the semiconductor chip IC8 a. Therefore, even if there is amanufacturing variation between the comparing circuit CN of thesemiconductor chip IC8 and the comparing circuit CNaa of thesemiconductor chip IC8 a, the lighting device 50 a can prevent avariation in timing of causing as well as stopping light emission of thelight emitting element groups HS and the light emitting element groupsHSa.

In addition, in the lighting device 50 a, the light emission control andthe light emission stop control of the light emitting element groups HSBare performed by the light emission control unit HC8 of thesemiconductor chip IC8 and the light emission control unit HC8 a of thesemiconductor chip IC8 a. Therefore, even if the wiring resistance ofthe wiring W2 for the semiconductor chip IC8 a to receive power supplyof the drive voltage Vk and the drive current Ik from the power supplycircuit VS is different from the wiring resistance of the wiring W1 forthe semiconductor chip IC8 to receive power supply of the drive voltageVk and the drive current Ik from the power supply circuit VS, thelighting device 50 a can prevent a variation in timing of causing aswell as stopping light emission of the light emitting element groups HSand the light emitting element groups HSa.

Second Variation of Fifth Embodiment

FIG. 27 is a diagram illustrating a lighting device 50 b according to asecond variation of the fifth embodiment of the present invention. Thelighting device 50 b includes the power supply circuit VS, the lightemitting element groups HSB, a semiconductor chip IC9 as the firstsemiconductor chip, and a semiconductor chip IC9 a as the secondsemiconductor chip. Note that in the lighting device 50 b illustrated inFIG. 27, the same structure as in the lighting device 20 a illustratedin FIG. 7, or the lighting device 50 illustrated in FIG. 25 is denotedby the same numeral or symbol, and description thereof is appropriatelyomitted.

The light emitting element groups HSB include the light emitting elementgroups HS and the light emitting element groups HSa. The light emittingelement groups HS include the light emitting element group HS1, and thelight emitting element group HS2 as the first light emitting elementgroup. The light emitting element groups HSa include the light emittingelement group HS11, and the light emitting element group HS12 as thesecond light emitting element group.

The semiconductor chip IC9 has electrode pads for external electricconnection, which include the electrode pad T1, the electrode pad T2,the electrode pad T3, the electrode pad T6, the electrode pad T7, theelectrode pad T8, and the electrode pad T9. In addition, thesemiconductor chip IC9 includes a light emission control unit HC9 as thefirst light emission control unit, the dimming circuit LC1, and thedimming circuit LC2 as the first dimming portion.

The electrode pad T1 is connected to the power supply circuit VS via thewiring W1 as the first power supply wiring. In other words, the wiringW1 is connected to the power supply circuit VS and the semiconductorchip IC9. The electrode pad T2 is connected to the node Nh1 of the lightemitting element group HS1. The electrode pad T3 is connected to thenode Nh2 of the light emitting element group HS2. The electrode pad T6is connected to one terminal of the node Nh1 a of the light emittingelement group HS1. The electrode pad T7 is connected to the node Nh2 aof the light emitting element group HS2.

The light emission control unit HC9 includes the comparing circuit CNaas the first comparing circuit, a detecting portion K2 as the firstdetecting portion, the transistor N1, and the transistor N2 as the firstcontrol switch.

The comparing circuit CNa is connected to the electrode pad T1, i.e.connected to the power supply circuit VS via the electrode pad T1. Thecomparing circuit CNa determines whether the drive voltage Vk is higheror lower than the light emission reference voltage VHa or a voltagebased on the light emission reference voltage VHa, and outputs a resultof the comparison as the comparison result signal Vcr2. Note that theoutput terminal of the comparing circuit CNa is connected to theelectrode pad T8.

The detecting portion K2 is an AND circuit having a first input terminaland a second input terminal, for example. The first input terminal ofthe detecting portion K2 is connected to the output terminal of thecomparing circuit CNa and is supplied with the comparison result signalVcr2. In addition, the first input terminal of the detecting portion K2is connected to the electrode pad T8, and the second input terminal isconnected to the electrode pad T9. The detecting portion K2 outputs anoutput signal Ko2, which is the logical product of the signal input tothe first input terminal and the signal input to the second inputterminal. Here, the connection node between the first input terminal ofthe detecting portion K2 and the comparing circuit CNa is referred to asa node Nd17. Note that the detecting portion K2 is not limited to theAND circuit but may be any other logic circuit, as long as it outputsthe output signal Ko2 as a result, which is the logical product of thesignal input to the first input terminal and the signal input to thesecond input terminal.

The transistor N1 is an NMOS transistor, which has the source terminal Sconnected to the power supply VSS, the drain terminal D connected to theelectrode pad T6, i.e. connected to the one terminal of the lightemitting element group HS1 via the electrode pad T6, and the gateterminal G connected to the output terminal of the detecting portion K1.The transistor N1 is on-off controlled by the output signal Ko2 suppliedfrom the detecting portion K2.

The dimming circuit LC1 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1. In addition, the dimming circuit LC1 has the other terminalconnected to the electrode pad T2, i.e. connected to the node Nh1 of thelight emitting element group HS1 via the electrode pad T2.

The dimming circuit LC2 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1. In addition, the dimming circuit LC2 has the other terminalconnected to the electrode pad T3, i.e. connected to the node Nh2 of thelight emitting element group HS2 via the electrode pad T3.

The semiconductor chip IC9 a has the same structure as the semiconductorchip IC9. However, in the semiconductor chip IC9 a of FIG. 27, forconvenience of description, in order to discriminate from thesemiconductor chip IC9, the suffix “a” is added to the numeral or symbolof the structure in the semiconductor chip IC9. In addition, in thesemiconductor chip IC9 a, description of the structure described in thesemiconductor chip IC9 is appropriately omitted. Note that the“comparing circuit CNa” is referred to as the “comparing circuit CNaaa”here, in order to discriminate from the “comparing circuit CNaa”illustrated in FIG. 25 or the like.

The semiconductor chip IC9 a has electrode pads for external electricconnection, which include the electrode pad T1 a, the electrode pad T2a, the electrode pad T3 a, the electrode pad T6 a, the electrode pad T7a, the electrode pad T8 a, and the electrode pad T9 a. In addition, thesemiconductor chip IC9 a includes a light emission control unit HC9 a asthe second light emission control unit, the dimming circuit LC1 a, andthe dimming circuit LC2 a as the second dimming portion. The lightemission control unit HC9 a includes the comparing circuit CNaaa as thesecond comparing circuit, a detecting portion K2 a as the seconddetecting portion, the transistor N1 a, and the transistor N2 a as thesecond control switch.

The electrode pad T1 a is connected to the power supply circuit VS viathe wiring W2 as the second power supply wiring. In other words, thewiring W2 is connected to the power supply circuit VS and thesemiconductor chip IC9 a. The electrode pad T2 a is connected to thenode Nh11 of the light emitting element group HS11. The electrode pad T3a is connected to the node Nh12 of the light emitting element groupHS12. The electrode pad T6 a is connected to the one terminal of thelight emitting element group HS11. The electrode pad T7 a is connectedto the one terminal of the light emitting element group HS12. Note thatthe wiring resistance of the wiring W2 may be different from the wiringresistance of the wiring W1.

The light emission control unit HC9 a includes the comparing circuitCNaaa as the second comparing circuit, the detecting portion K2 a as thesecond detecting portion, the transistor N1 a, and the transistor N2 aas the second control switch.

The dimming circuit LC11 has one terminal connected to the electrode padT1 a, i.e. connected to the power supply circuit VS via the electrodepad T1 a. In addition, the dimming circuit LC11 has the other terminalconnected to the electrode pad T2 a, i.e. connected to the node Nh11 ofthe light emitting element group HS11 via the electrode pad T2 a.

The dimming circuit LC12 has one terminal connected to the electrode padT1 a, i.e. connected to the power supply circuit VS via the electrodepad T1 a. In addition, the dimming circuit LC12 has the other terminalconnected to the electrode pad T3 a, i.e. connected to the node Nh12 ofthe light emitting element group HS12 via the electrode pad T3 a.

The electrode pad T8 a is connected to the electrode pad T9 of thesemiconductor chip IC9 via the wiring W4 as the second connectionwiring. In other words, the wiring W4 electrically connects the nodeNd17 a and the second input terminal of the detecting portion K2.

The electrode pad T9 a is connected to the electrode pad T8 of thesemiconductor chip IC9 via the wiring W5 as the third connection wiring.In other words, the wiring W5 electrically connects the node Nd17 andthe second input terminal of the detecting portion K2 a.

Here, in the detecting portion K2 of the semiconductor chip IC9, thefirst input terminal is supplied with the comparison result signal Vcr2output from the comparing circuit CNa, the second input terminal issupplied with comparison result signal Vcr2 a output from the comparingcircuit CNaaa of the semiconductor chip IC9 a, and the logical sum ofthese signals is supplied to the gate terminals G of the transistor N1and the transistor N2 as the output signal Ko2 as the first outputsignal so that the transistor N1 and the transistor N2 are on-offcontrolled. In other words, the light emission control and the lightemission stop control of the light emitting element groups HS areperformed by the light emission control unit HC9 and the light emissioncontrol unit HC9 a of the semiconductor chip IC9 a.

In addition, in the detecting portion K2 a of the semiconductor chip IC9a, the first input terminal is supplied with the comparison resultsignal Vcr2 output from the comparing circuit CNa of the semiconductorchip IC9, the second input terminal is supplied with the comparisonresult signal Vcr2 a output from the comparing circuit CNaaa, and thelogical sum of these signals is supplied to the gate terminals G of thetransistor N1 a and the transistor N2 a as an output signal Ko2 a as thesecond output signal so that the transistor N1 a and the transistor N2 aare on-off controlled. In other words, the light emission control andthe light emission stop control of the light emitting element groups HSaare performed by the light emission control unit HC9 a and the lightemission control unit HC9 of the semiconductor chip IC9.

Here, the on/off states of the transistor N1 and the transistor N2 aredetermined by the signal level of the output signal Ko2 of the detectingportion K2 and the signal level of the output signal Ko2 a of thedetecting portion K2 a. Further, the signal level of the output signalKo2 of the detecting portion K2 and the signal level of the outputsignal Ko2 a of the detecting portion K2 a are determined by the levelof the comparison result signal Vcr2 output from the comparing circuitCNa and the level of the comparison result signal Vcr2 a output from thecomparing circuit CNaaa.

If each of the comparing circuit CNa and the comparing circuit CNaaadetermines that the drive voltage Vk is lower than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr2 and the comparison resultsignal Vcr2 a become low level. Therefore, the first input terminal andthe second input terminal of each of the detecting portion K2 and thedetecting portion K2 a are supplied with the low level signal, and hencethe output signal Ko2 and the output signal Ko2 a become low level. Inthis case, the gate terminals G of the transistor N1, the transistor N2,the transistor N1 a, and the transistor N2 a are supplied with the lowlevel signal, the transistor N1, the transistor N2, the transistor N1 a,and the transistor N2 a are all turned off.

If the comparing circuit CNa determines that the drive voltage Vk islower than the light emission reference voltage VHa or a voltage basedon the light emission reference voltage VHa, while the comparing circuitCNaaa determines that the drive voltage Vk is higher than the lightemission reference voltage VHa or a voltage based on the light emissionreference voltage VHa, the comparison result signal Vcr2 becomes lowlevel, while the comparison result signal Vcr2 a becomes high level. Inthis case, the second input terminal of the detecting portion K2 and thefirst input terminal of the detecting portion K2 a are both suppliedwith the high level signal, while the first input terminal of thedetecting portion K2 and the second input terminal of the detectingportion K2 a are both supplied with the low level signal. Therefore, theoutput signal Ko2 and the output signal Ko2 a become low level. In thiscase, the gate terminals G of the transistor N1, the transistor N2, thetransistor N1 a, and the transistor N2 a are supplied with the highlevel signal, and hence the transistor N1, the transistor N2, thetransistor N1 a, and the transistor N2 a are all turned off.

If each of the comparing circuit CNa and the comparing circuit CNaaadetermines that the drive voltage Vk is higher than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr2 and the comparison resultsignal Vcr2 a become high level. Therefore, the first input terminal andthe second input terminal of each of the detecting portion K2 and thedetecting portion K2 a are supplied with the high level signal, andhence the output signal Ko2 and the output signal Ko2 a become highlevel. In this case, the gate terminals G of the transistor N1, thetransistor N2, the transistor N1 a, and the transistor N2 a are suppliedwith the low level signal, and hence the transistor N1, the transistorN2, the transistor N1 a, and the transistor N2 a are all turned on.

As described above, in the lighting device 50 b, the light emissioncontrol and the light emission stop control of the light emittingelement groups HSB are performed by the light emission control unit HC9of the semiconductor chip IC9 and the light emission control unit HC9 aof the semiconductor chip IC9 a. Therefore, even if there is amanufacturing variation between the comparing circuit CNa of thesemiconductor chip IC9 and the comparing circuit CNaaa of thesemiconductor chip IC9 a, the lighting device 50 b can prevent avariation in timing of causing as well as stopping light emission of thelight emitting element groups HS and the light emitting element groupsHSa.

In addition, in the lighting device 50 b, the light emission control andthe light emission stop control of the light emitting element groups HSBare performed by the light emission control unit HC9 of thesemiconductor chip IC9 and the light emission control unit HC9 a of thesemiconductor chip IC9 a. Therefore, even if the wiring resistance ofthe wiring W2 for the semiconductor chip IC9 a to receive power supplyof the drive voltage Vk and the drive current Ik from the power supplycircuit VS is different from the wiring resistance of the wiring W1 forthe semiconductor chip IC9 to receive power supply of the drive voltageVk and the drive current Ik from the power supply circuit VS, thelighting device 50 b can prevent a variation in timing of causing aswell as stopping light emission of the light emitting element groups HSand the light emitting element groups HSa.

Third Variation of Fifth Embodiment

FIG. 28 is a diagram illustrating a lighting device 50 c according to athird variation of the fifth embodiment of the present invention. Thelighting device 50 c includes the power supply circuit VS, the lightemitting element groups HSB, a semiconductor chip IC10 as the firstsemiconductor chip, and a semiconductor chip IC10 a as the secondsemiconductor chip. Note that in the lighting device 50 c illustrated inFIG. 28, the same structure as in the lighting device 30 illustrated inFIG. 8, the lighting device 30 a illustrated in FIG. 10, the lightingdevice 50 a illustrated in FIG. 25, or the lighting device 50 cillustrated in FIG. 27 is denoted by the same numeral or symbol, anddescription thereof is appropriately omitted.

The light emitting element groups HSB include the light emitting elementgroups HS and the light emitting element groups HSa. The light emittingelement groups HS include the light emitting element group HS1, and thelight emitting element group HS2 as the first light emitting elementgroup. The light emitting element groups HSa include the light emittingelement group HS11 and the light emitting element group HS12 as thesecond light emitting element group.

The semiconductor chip IC10 has electrode pads for external electricconnection, which include the electrode pad T1, the electrode pad T2,the electrode pad T3, the electrode pad T8, and the electrode pad T9. Inaddition, the semiconductor chip IC10 includes a light emission controlunit HC10 as the first light emission control unit, the dimming circuitLC1, and the dimming circuit LC2 as the first dimming portion. The lightemission control unit HC10 includes the comparing circuit CNa as thefirst comparing circuit, the detecting portion K2 as the first detectingportion, the transistor P6, and the transistor P7 as the first controlswitch.

The electrode pad T1 is connected to the power supply circuit VS via thewiring W1 as the first power supply wiring. In other words, the wiringW1 is connected to the power supply circuit VS and the semiconductorchip IC10. The electrode pad T2 is connected to the node Nh1 of thelight emitting element group HS1. The electrode pad T3 is connected tothe node Nh2 of the light emitting element group HS2.

The transistor P6 is a PMOS transistor, which has the source terminal Sconnected to the electrode pad T1, i.e. connected to the power supplycircuit VS via the electrode pad T1, the drain terminal D connected toone terminal of the dimming circuit LC1, and the gate terminal Gconnected to the output terminal of the detecting portion K2. Thetransistor P6 is on-off controlled by the output signal Ko2 suppliedfrom the detecting portion K2.

The transistor P7 is a PMOS transistor, which has the source terminal Sconnected to the electrode pad T1, i.e. connected to the power supplycircuit VS via the electrode pad T1, the drain terminal D connected toone terminal of the dimming circuit LC2, and the gate terminal Gconnected to the output terminal of the detecting portion K2. Thetransistor P7 is on-off controlled by the output signal Ko2 suppliedfrom the detecting portion K2.

The dimming circuit LC1 has the other terminal connected to theelectrode pad T2, i.e. connected to the node Nh1 of the light emittingelement group HS1 via the electrode pad T2.

The dimming circuit LC2 has the other terminal connected to theelectrode pad T3, i.e. connected to the node Nh2 of the light emittingelement group HS2 via the electrode pad T3.

The semiconductor chip IC10 a has the same structure as thesemiconductor chip IC10. However, in the semiconductor chip IC10 a ofFIG. 28, for convenience of description, in order to discriminate fromthe semiconductor chip IC10, the suffix “a” is added to the numeral orsymbol of the structure in the semiconductor chip IC10. In addition, inthe semiconductor chip IC10 a, the structure described in thesemiconductor chip IC10 is appropriately omitted. Note that the“comparing circuit CNa” is referred to as the “comparing circuit CNaaa”here, in order to discriminate from the “comparing circuit CNaa”illustrated in FIG. 25 or the like.

The semiconductor chip IC10 a has electrode pads for external electricconnection, which include the electrode pad T1 a, the electrode pad T2a, the electrode pad T3 a, the electrode pad T8 a, and the electrode padT9 a. In addition, the semiconductor chip IC10 a includes a lightemission control unit HC10 a as the second light emission control unit,the dimming circuit LC1 a, and the dimming circuit LC2 a as the seconddimming portion. The light emission control unit HC10 a includes thecomparing circuit CNaaa as the second comparing circuit, the detectingportion K2 a as the second detecting portion, the transistor N1 a, andthe transistor N2 a as the second control switch.

The electrode pad T1 a is connected to the power supply circuit VS viathe wiring W2 as the second power supply wiring. In other words, thewiring W2 is connected to the power supply circuit VS and thesemiconductor chip IC10 a. The electrode pad T2 a is connected to thenode Nh11 of the light emitting element group HS11. The electrode pad T3a is connected to the node Nh12 of the light emitting element groupHS12. Note that the wiring resistance of the wiring W2 may be differentfrom the wiring resistance of the wiring W1.

The light emission control unit HC10 a includes the comparing circuitCNaaa as the second comparing circuit, the detecting portion K2 a as thesecond detecting portion, the transistor P6 a, and the transistor P7 aas the second control switch.

The dimming circuit LC11 has the other terminal connected to theelectrode pad T2 a, i.e. connected to the node Nh11 of the lightemitting element group HS11 via the electrode pad T2 a.

The dimming circuit LC12 has the other terminal connected to theelectrode pad T3 a, i.e. connected to the node Nh12 of the lightemitting element group HS12 via the electrode pad T3 a.

The electrode pad T8 a is connected to the electrode pad T9 of thesemiconductor chip IC10 via the wiring W4 as the second connectionwiring. In other words, the wiring W4 electrically connects the nodeNd17 a and the second input terminal of the detecting portion K2.

The electrode pad T9 a is connected to the electrode pad T8 of thesemiconductor chip IC10 via the wiring W5 as the third connectionwiring. In other words, the wiring W5 electrically connects the nodeNd17 and the second input terminal of the detecting portion K2 a.

Here, in the detecting portion K2 of the semiconductor chip IC10, thefirst input terminal is supplied with the comparison result signal Vcr2output from the comparing circuit CNa, the second input terminal issupplied with the comparison result signal Vcr2 a output from thecomparing circuit CNaaa of the semiconductor chip IC10 a, and thelogical sum of these signals is supplied to the gate terminals G of thetransistor P6 and the transistor P7 as the output signal Ko2 as thefirst output signal so that the transistor P6 and the transistor P7 areon-off controlled. In other words, the light emission control and thelight emission stop control of the light emitting element groups HS areperformed by the light emission control unit HC10 and the light emissioncontrol unit HC10 a of the semiconductor chip IC10 a.

In addition, in the detecting portion K2 a of the semiconductor chipIC10 a, the first input terminal is supplied with the comparison resultsignal Vcr2 output from the comparing circuit CNa of the semiconductorchip IC10, the second input terminal is supplied with the comparisonresult signal Vcr2 a output from the comparing circuit CNaaa, and thelogical sum of these signals is supplied to the gate terminals G of thetransistor N1 a and the transistor N2 a as the output signal Ko2 a asthe second output signal, so that the transistor P6 a and the transistorP7 a are on-off controlled. In other words, the light emission controland the light emission stop control of the light emitting element groupsHSa are performed by the light emission control unit HC10 a and thelight emission control unit HC10 of the semiconductor chip IC10.

Here, the on/off states of the transistor P6 and the transistor P7 aredetermined by the signal level of the output signal Ko2 of the detectingportion K2 and the signal level of the output signal Ko2 a of thedetecting portion K2 a. Further, the signal level of the output signalKo2 of the detecting portion K2 and the signal level of the outputsignal Ko2 a of the detecting portion K2 a are determined by the levelof the comparison result signal Vcr2 output from the comparing circuitCNa and the level of the comparison result signal Vcr2 a output from thecomparing circuit CNaaa.

If each of the comparing circuit CNa and the comparing circuit CNaaadetermines that the drive voltage Vk is lower than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr2 and the comparison resultsignal Vcr2 a become low level. Therefore, the first input terminal andthe second input terminal of each of the detecting portion K2 and thedetecting portion K2 a are supplied with the low level signal, and hencethe output signal Ko2 and the output signal Ko2 a become low level. Inthis case, the gate terminals G of the transistor P6, the transistor P7,the transistor P6 a, and the transistor P7 a are supplied with the lowlevel signal, and hence the transistor P6, the transistor P7, thetransistor P6 a, and the transistor P7 a are all turned on.

If the comparing circuit CNa determines that the drive voltage Vk islower than the light emission reference voltage VHa or a voltage basedon the light emission reference voltage VHa, while the comparing circuitCNaaa determines that the drive voltage Vk is higher than the lightemission reference voltage VHa or a voltage based on the light emissionreference voltage VHa, the comparison result signal Vcr2 becomes lowlevel, while the comparison result signal Vcr2 a becomes high level. Inthis case, the second input terminal of the detecting portion K2 and thefirst input terminal of the detecting portion K2 a are both suppliedwith the high level signal, while the first input terminal of thedetecting portion K2 and the second input terminal of the detectingportion K2 a are both supplied with the low level signal. Therefore, theoutput signal Ko2 and the output signal Ko2 a become low level. In thiscase, the gate terminals G of the transistor P6, the transistor P7, thetransistor P6 a, and the transistor P7 a are supplied with the highlevel signal, and hence the transistor P6, the transistor P7, thetransistor P6 a, and the transistor P7 a are all turned on.

If each of the comparing circuit CNa and the comparing circuit CNaaadetermines that the drive voltage Vk is higher than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr2 and the comparison resultsignal Vcr2 a become high level. Therefore, the first input terminal andthe second input terminal of each of the detecting portion K2 and thedetecting portion K2 a are supplied with the high level signal so thatthe output signal Ko2 and the output signal Ko2 a become high level. Inthis case, the gate terminals G of the transistor P6, the transistor P7,the transistor P6 a, and the transistor P7 a are supplied with the lowlevel signal, and hence the transistor P6, the transistor P7, thetransistor P6 a, and the transistor P7 a are all turned off.

As described above, in the lighting device 50 c, the light emissioncontrol and the light emission stop control of the light emittingelement groups HSB are performed by the light emission control unit HC10of the semiconductor chip IC10 and the light emission control unit HC10a of the semiconductor chip IC10 a. Therefore, even if there is amanufacturing variation between the comparing circuit CNa of thesemiconductor chip IC10 and the comparing circuit CNaaa of semiconductorchip IC10 a, the lighting device 50 c can prevent a variation in timingof causing as well as stopping light emission of the light emittingelement groups HS and the light emitting element groups HSa.

In addition, in the lighting device 50 c, the light emission control andthe light emission stop control of the light emitting element groups HSBare performed by the light emission control unit HC10 of thesemiconductor chip IC10 and the light emission control unit HC10 a ofthe semiconductor chip IC10 a. Therefore, even if the wiring resistanceof the wiring W2 for the semiconductor chip IC10 a to receive powersupply of the drive voltage Vk and the drive current Ik from the powersupply circuit VS is different from the wiring resistance of the wiringW1 for the semiconductor chip IC10 to receive power supply of the drivevoltage Vk and the drive current Ik from the power supply circuit VS,the lighting device 50 c can prevent a variation in timing of causing aswell as stopping light emission of the light emitting element groups HSand the light emitting element groups HSa.

Fourth Variation of Fifth Embodiment

FIG. 29 is a diagram illustrating a lighting device 50 d according to afourth variation of the fifth embodiment of the present invention. Thelighting device 50 d includes the power supply circuit VS, the lightemitting element groups HSB, a semiconductor chip IC11 as the firstsemiconductor chip, and a semiconductor chip IC11 a as the secondsemiconductor chip. Note that in the lighting device 50 d illustrated inFIG. 29, the same structure as in the lighting device 30 b illustratedin FIG. 11 or the lighting device 50 d illustrated in FIG. 28 is denotedby the same numeral or symbol, and description thereof is appropriatelyomitted.

The light emitting element groups HSB include the light emitting elementgroups HS and the light emitting element groups HSa. The light emittingelement groups HS include the light emitting element group HS1, and thelight emitting element group HS2 as the first light emitting elementgroup. The light emitting element groups HSa include the light emittingelement group HS11 and the light emitting element group HS12 as thesecond light emitting element group.

The semiconductor chip IC11 has electrode pads for external electricconnection, which include the electrode pad T1, the electrode pad T2,the electrode pad T3, the electrode pad T8, and the electrode pad T9. Inaddition, the semiconductor chip IC11 includes the light emissioncontrol unit HC11 as the first light emission control unit, the dimmingcircuit LC1, and the dimming circuit LC2 as the first dimming portion.The light emission control unit HC11 includes the comparing circuit CNaas the first comparing circuit, the detecting portion K2 as the firstdetecting portion, the transistor N3, and the transistor N4 as the firstcontrol switch.

The electrode pad T1 is connected to the power supply circuit VS via thewiring W1 as the first power supply wiring. In other words, the wiringW1 is connected to the power supply circuit VS and the semiconductorchip IC11. The electrode pad T2 is connected to the node Nh1 of thelight emitting element group HS1. The electrode pad T3 is connected tothe node Nh2 of the light emitting element group HS2.

The transistor N3 is an NMOS transistor, which has the source terminal Sconnected to the dimming circuit LC1, the drain terminal D connected tothe power supply VSS, and the gate terminal G connected to the outputterminal of the detecting portion K2. The transistor N3 is on-offcontrolled by the output signal Ko2 supplied from the detecting portionK2.

The transistor N4 is an NMOS transistor, which has the source terminal Sconnected to the dimming circuit LC2, the drain terminal D connected tothe power supply VSS, and the gate terminal G connected to the outputterminal of the detecting portion K2. The transistor N4 is on-offcontrolled by the output signal Ko2 supplied from the detecting portionK2.

The dimming circuit LC1 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1, and the other terminal connected to the electrode pad T2, i.e.connected to the node Nh1 of the light emitting element group HS1 viathe electrode pad T2.

The dimming circuit LC2 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1, the other terminal connected to the electrode pad T3, i.e. connectedto the node Nh2 of the light emitting element group HS2 via theelectrode pad T3.

The semiconductor chip IC11 a has the same structure as thesemiconductor chip IC11. However, in the semiconductor chip IC11 a ofFIG. 29, for convenience of description, in order to discriminate fromthe semiconductor chip IC11, the suffix “a” is added to the numeral orsymbol of the structure in the semiconductor chip IC11. In addition, inthe semiconductor chip IC11 a, the structure described in thesemiconductor chip IC11 is appropriately omitted. Note that the“comparing circuit CNa” is referred to as a “comparing circuit CNaaa”here, in order to discriminate from the “comparing circuit CNaa”illustrated in FIG. 25 or the like.

The semiconductor chip IC11 a has electrode pads for external electricconnection, which include the electrode pad T1 a, the electrode pad T2a, the electrode pad T3 a, the electrode pad T8 a, and the electrode padT9 a. In addition, the semiconductor chip IC11 a includes a lightemission control unit HC11 a as the second light emission control unit,the dimming circuit LC1 a, and the dimming circuit LC2 a as the seconddimming portion. The light emission control unit HC11 a includes thecomparing circuit CNaaa as the second comparing circuit, the detectingportion K2 a as the second detecting portion, the transistor N3 a, andthe transistor N4 a as the second control switch.

The electrode pad T1 a is connected to the power supply circuit VS viathe wiring W2 as the second power supply wiring. In other words, thewiring W2 is connected to the power supply circuit VS and thesemiconductor chip IC11 a. The electrode pad T2 a is connected to thenode Nh11 of the light emitting element group HS11. The electrode pad T3a is connected to the node Nh12 of the light emitting element groupHS12. Note that the wiring resistance of the wiring W2 may be differentfrom the wiring resistance of the wiring W1.

The dimming circuit LC11 has one terminal connected to the electrode padT1 a, i.e. connected to the power supply circuit VS via the electrodepad T1 a, and the other terminal connected to the electrode pad T2 a,i.e. connected to the node Nh11 of the light emitting element group HS11via the electrode pad T2 a.

The dimming circuit LC12 has one terminal connected to the electrode padT1 a, i.e. connected to the power supply circuit VS via the electrodepad T1 a, and the other terminal connected to the electrode pad T3 a,i.e. connected to the node Nh12 of the light emitting element group HS12via the electrode pad T3 a.

The electrode pad T8 a is connected to the electrode pad T9 of thesemiconductor chip IC11 via the wiring W4 as the second connectionwiring. In other words, the wiring W4 electrically connects the nodeNd17 a and the second input terminal of the detecting portion K2.

The electrode pad T9 a is connected to the electrode pad T8 of thesemiconductor chip IC11 via the wiring W5 as the third connectionwiring. In other words, the wiring W5 electrically connects the nodeNd17 and the second input terminal of the detecting portion K2 a.

Here, in the detecting portion K2 of the semiconductor chip IC11, thefirst input terminal is supplied with the comparison result signal Vcr2output from the comparing circuit CNa, the second input terminal issupplied with the comparison result signal Vcr2 a output from thecomparing circuit CNaaa of the semiconductor chip IC11 a, and thelogical sum of these signals is supplied to the gate terminals G of thetransistor N3 and the transistor N4 as the output signal Ko2 as thefirst output signal so that the transistor N3 and the transistor N4 areon-off controlled. In other words, the light emission control and thelight emission stop control of the light emitting element groups HS areperformed by the light emission control unit HC11 and the light emissioncontrol unit HC11 a of the semiconductor chip IC11 a.

In addition, in the detecting portion K2 a of the semiconductor chipIC11 a, the first input terminal is supplied with the comparison resultsignal Vcr2 output from the comparing circuit CNa of the semiconductorchip IC11, the second input terminal is supplied with the comparisonresult signal Vcr2 a output from the comparing circuit CNaaa, and thelogical sum of these signals is supplied to the gate terminals G of thetransistor N1 a and the transistor N2 a as the output signal Ko2 a asthe second output signal so that the transistor N3 a and the transistorN4 a are on-off controlled. In other words, the light emission controland the light emission stop control of the light emitting element groupsHSa are performed by the light emission control unit HC11 a and thelight emission control unit HC11 of the semiconductor chip IC11.

Here, the on/off states of the transistor N3 and the transistor N4 aredetermined by the signal level of the output signal Ko2 of the detectingportion K2 and the signal level of the output signal Ko2 a of thedetecting portion K2 a. Further, the signal level of the output signalKo2 of the detecting portion K2 and the signal level of the outputsignal Ko2 a of the detecting portion K2 a are determined by the levelof the comparison result signal Vcr2 output from the comparing circuitCNa and the level of the comparison result signal Vcr2 a output from thecomparing circuit CNaaa.

If each of the comparing circuit CNa and the comparing circuit CNaaadetermines that the drive voltage Vk is lower than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr2 and the comparison resultsignal Vcr2 a become low level. Therefore, the first input terminal andthe second input terminal of each of the detecting portion K2 and thedetecting portion K2 a are supplied with the low level signal, and hencethe output signal Ko2 and the output signal Ko2 a become low level. Inthis case, the gate terminals G of the transistor N3, the transistor N4,the transistor N3 a, and the transistor N4 a are supplied with the lowlevel signal, and hence the transistor N3, the transistor N4, thetransistor N3 a, and the transistor N4 a are all turned off.

If the comparing circuit CNa determines that the drive voltage Vk islower than the light emission reference voltage VHa or a voltage basedon the light emission reference voltage VHa, while the comparing circuitCNaaa determines that the drive voltage Vk is higher than the lightemission reference voltage VHa or a voltage based on the light emissionreference voltage VHa, the comparison result signal Vcr2 becomes lowlevel, while the comparison result signal Vcr2 a becomes high level. Inthis case, the second input terminal of the detecting portion K2 and thefirst input terminal of the detecting portion K2 a are both suppliedwith the high level signal, while the first input terminal of thedetecting portion K2 and the second input terminal of the detectingportion K2 a are both supplied with the low level signal. Therefore, theoutput signal Ko2 and the output signal Ko2 a become low level. In thiscase, the gate terminals G of the transistor N3, the transistor N4, thetransistor N3 a, and the transistor N4 a are supplied with the highlevel signal, and hence the transistor N3, the transistor N4, thetransistor N3 a, and the transistor N4 a are all turned off.

If each of the comparing circuit CNa and the comparing circuit CNaaadetermines that the drive voltage Vk is higher than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr2 and the comparison resultsignal Vcr2 a become high level. Therefore, the first input terminal andthe second input terminal of each of the detecting portion K2 and thedetecting portion K2 a are supplied with the high level signal so thatthe output signal Ko2 and the output signal Ko2 a become high level. Inthis case, the gate terminals G of the transistor N3, the transistor N4,the transistor N3 a, and the transistor N4 a are supplied with the lowlevel signal, and hence the transistor N3, the transistor N4, thetransistor N3 a, and the transistor N4 a are all turned on.

As described above, in the lighting device 50 d, the light emissioncontrol and the light emission stop control of the light emittingelement groups HSB are performed by the light emission control unit HC11of the semiconductor chip IC11 and the light emission control unit HC11a of the semiconductor chip IC11 a. Therefore, even if there is amanufacturing variation between the comparing circuit CNa of thesemiconductor chip IC11 and the comparing circuit CNaaa of thesemiconductor chip IC11 a, the lighting device 50 d can prevent avariation in timing of causing as well as stopping light emission of thelight emitting element groups HS and the light emitting element groupsHSa.

In addition, in the lighting device 50 d, the light emission control andthe light emission stop control of the light emitting element groups HSBare performed by the light emission control unit HC11 of thesemiconductor chip IC11 and the light emission control unit HC11 a ofthe semiconductor chip IC11 a. Therefore, even if the wiring resistanceof the wiring W2 for the semiconductor chip IC11 a to receive powersupply of the drive voltage Vk and the drive current Ik from the powersupply circuit VS is different from the wiring resistance of the wiringW1 for the semiconductor chip IC10 to receive power supply of the drivevoltage Vk and the drive current Ik from the power supply circuit VS,the lighting device 50 d can prevent a variation in timing of causing aswell as stopping light emission of the light emitting element groups HSand the light emitting element groups HSa.

Fifth Variation of Fifth Embodiment

FIG. 30 is a diagram illustrating a lighting device 50 e according to afifth variation of the fifth embodiment of the present invention. Thelighting device 50 e includes the power supply circuit VS, the lightemitting element groups HSB, a semiconductor chip IC12 as the firstsemiconductor chip, and a semiconductor chip IC12 a as the secondsemiconductor chip. Note that in the lighting device 50 e illustrated inFIG. 30, the same structure as in the lighting device 30 c illustratedin FIG. 12 or the lighting device 50 illustrated in FIG. 25 is denotedby the same numeral or symbol, and description thereof is appropriatelyomitted.

The light emitting element groups HSB include the light emitting elementgroups HS and the light emitting element groups HSa. The light emittingelement groups HS include the light emitting element group HS1, and thelight emitting element group HS2 as the first light emitting elementgroup. The light emitting element groups HSa include the light emittingelement group HS11, and the light emitting element group HS12 as thesecond light emitting element group.

The semiconductor chip IC12 has electrode pads for external electricconnection, which include the electrode pad T1, the electrode pad T2,the electrode pad T3, the electrode pad T6, the electrode pad T7, theelectrode pad T8, and the electrode pad T9. In addition, thesemiconductor chip IC12 includes the light emission control unit HC12 asthe first light emission control unit, the dimming circuit LC11, and thedimming circuit LC12 as the first dimming portion.

The electrode pad T1 is connected to the power supply circuit VS via thewiring W1 as the first power supply wiring. In other words, the wiringW1 is connected to the power supply circuit VS and the semiconductorchip IC12. The electrode pad T2 is connected to the node Nh1 of thelight emitting element group HS1. The electrode pad T3 is connected tothe node Nh2 of the light emitting element group HS2. The electrode padT6 is connected to the one terminal of the light emitting element groupHS1. The electrode pad T7 is connected to the one terminal of the lightemitting element group HS2.

The dimming circuit LC11 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1. In addition, the dimming circuit LC11 has the other terminalconnected to the electrode pad T2, i.e. connected to the node Nh1 of thelight emitting element group HS1 via the electrode pad T2, and the otherterminal connected to the electrode pad T6, i.e. connected to the nodeNd8 of the light emitting element group HS1 via the electrode pad T6.Note that the dimming circuit LC11 includes a transistor N5 and thedriving circuit KD1 illustrated in FIG. 12.

The dimming circuit LC12 has one terminal connected to the electrode padT1, i.e. connected to the power supply circuit VS via the electrode padT1. In addition, the dimming circuit LC12 has the other terminalconnected to the electrode pad T3, i.e. connected to the node Nh2 of thelight emitting element group HS2 via the electrode pad T3, and the otherterminal connected to the electrode pad T7, i.e. connected to the nodeNd9 of the light emitting element group HS2 via the electrode pad T7.Note that the dimming circuit LC12 includes a transistor N6 and thedriving circuit KD2 illustrated in FIG. 12.

The light emission control unit HC12 includes the comparing circuit CNas the first comparing circuit, and the detecting portion K1. The outputterminal of the detecting portion K1 is connected to the driving circuitKD1 of the dimming circuit LC11 and the driving circuit KD2 of thedimming circuit 12. In other words, the output terminal of the comparingcircuit CN is connected to the driving circuit KD1 of the dimmingcircuit LC11 and the driving circuit KD2 of the dimming circuit 12 viathe output terminal of the detecting portion K1. The output signal Ko1of the detecting portion K1 is supplied to the driving circuit KD1 andthe driving circuit KD2.

The semiconductor chip IC12 a has the same structure as thesemiconductor chip IC12. However, in the semiconductor chip IC12 a ofFIG. 30, for convenience of description, in order to discriminate fromthe semiconductor chip IC12, the suffix “a” is added to the numeral orsymbol of the structure in the semiconductor chip IC12. In addition, inthe semiconductor chip IC12 a, the structure described in thesemiconductor chip IC12 is appropriately omitted. Note that the“comparing circuit CN” is referred to as a “comparing circuit CNaa”here, in order to discriminate from the “comparing circuit CNa”illustrated in FIG. 5 or the like.

The semiconductor chip IC12 a has electrode pads for external electricconnection, which include the electrode pad T1 a, the electrode pad T2a, the electrode pad T3 a, the electrode pad T6 a, the electrode pad T7a, the electrode pad T8 a, and the electrode pad T9 a. In addition, thesemiconductor chip IC12 a includes a light emission control unit HC12 aas the second light emission control unit, the dimming circuit LC11 a,and the dimming circuit LC12 a as the second dimming portion.

The electrode pad T1 a is connected to the power supply circuit VS viathe wiring W2 as the second power supply wiring. In other words, thewiring W2 is connected to the power supply circuit VS and thesemiconductor chip IC12 a. The electrode pad T2 a is connected to thenode Nh11 of the light emitting element group HS11. The electrode pad T3a is connected to the node Nh12 of the light emitting element groupHS12. Note that the wiring resistance of the wiring W2 may be differentfrom the wiring resistance of the wiring W1.

The dimming circuit LC11 a has one terminal connected to the electrodepad T1 a, i.e. connected to the power supply circuit VS via theelectrode pad T1 a. In addition, the dimming circuit LC11 a has theother terminal connected to the electrode pad T2 a, i.e. connected tothe node Nh11 of the light emitting element group HS11 via the electrodepad T2 a, and the other terminal connected to the electrode pad T6 a,i.e. connected to the node Nd8 a of the light emitting element groupHS11 via the electrode pad T6 a. Note that the dimming circuit LC11 aincludes the driving circuit KD1 a and the transistor N5 a.

The dimming circuit LC12 a has one terminal connected to the electrodepad T1 a, i.e. connected to the power supply circuit VS via theelectrode pad T1 a. In addition, the dimming circuit LC12 a has theother terminal connected to the electrode pad T3 a, i.e. connected tothe node Nh12 of the light emitting element group HS12 via the electrodepad T3 a, and the other terminal connected to the electrode pad T7 a,i.e. connected to the node Nd9 a of the light emitting element groupHS12 via the electrode pad T7 a. Note that the dimming circuit LC12 aincludes the driving circuit KD2 a and a transistor N6 a.

The light emission control unit HC12 a includes the comparing circuitCNaa as the second comparing circuit, and the detecting portion K1 a asthe second detecting portion. The output terminal of the detectingportion K1 a is connected to the driving circuit KD1 a of the dimmingcircuit LC11 a and the driving circuit KD2 a of the dimming circuit 12a. In other words, the output terminal of the comparing circuit CNaa isconnected to the driving circuit KD1 a of the dimming circuit LC11 a andthe driving circuit KD2 a of the dimming circuit 12 a via the outputterminal of the detecting portion K1 a. The output signal Ko1 a of thedetecting portion K1 a is supplied to the driving circuit KD1 a and thedriving circuit KD2 a.

The electrode pad T8 a is connected to the electrode pad T9 of thesemiconductor chip IC12 via the wiring W4 as the second connectionwiring. In other words, the wiring W4 electrically connects the nodeNd16 a and the second input terminal of the detecting portion K1.

The electrode pad T9 a is connected to the electrode pad T8 of thesemiconductor chip IC12 via the wiring W5 as the third connectionwiring. In other words, the wiring W5 electrically connects the nodeNd16 and the second input terminal of the detecting portion K1 a.

Here, in the detecting portion K1 of the semiconductor chip IC12, thefirst input terminal is supplied with the comparison result signal Vcr1output from the comparing circuit CN, the second input terminal issupplied with the comparison result signal Vcr1 a output from thecomparing circuit CNaa of the semiconductor chip IC12 a, and the logicalsum of these signals is supplied to the driving circuit KD1 and thedriving circuit KD2 as the output signal Ko1 as the first output signal,so that outputs of the driving circuit KD1 and the driving circuit KD2are controlled. In other words, the light emission control and the lightemission stop control of the light emitting element groups HS areperformed by the light emission control unit HC12 and the light emissioncontrol unit HC12 a of the semiconductor chip IC12 a.

In addition, in the detecting portion K1 a of the semiconductor chipIC12 a, the first input terminal is supplied with the comparison resultsignal Vcr1 output from the comparing circuit CN of the semiconductorchip IC12, the second input terminal is supplied with the comparisonresult signal Vcr1 a output from the comparing circuit CNaa, and thelogical sum of these signals is supplied to the driving circuit KD1 aand the driving circuit KD2 a as the output signal Ko1 a as the secondoutput signal, so that outputs of the driving circuit KD1 a and thedriving circuit KD2 a are controlled. In other words, the light emissioncontrol and the light emission stop control of the light emittingelement groups HSa are performed by the light emission control unit HC12a and the light emission control unit HC12 of the semiconductor chipIC12.

Here, the outputs of the driving circuit KD1 and the driving circuit KD2are determined by the signal level of the output signal Ko1 of thedetecting portion K1 and the signal level of the output signal Ko1 a ofthe detecting portion K1 a. Further, the signal level of the outputsignal Ko1 of the detecting portion K1 and the signal level of theoutput signal Ko1 a of the detecting portion K1 a are determined by thelevel of the comparison result signal Vcr1 output from the comparingcircuit CN and the level of the comparison result signal Vcr1 a outputfrom the comparing circuit CNaa.

If each of the comparing circuit CN and the comparing circuit CNaadetermines that the drive voltage Vk is lower than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr1 and the comparison resultsignal Vcr1 a become high level. Therefore, the first input terminal andthe second input terminal of each of the detecting portion K1 and thedetecting portion K1 a are both supplied with the high level signal, andthe output signal Ko1 and the output signal Ko1 a become high level. Inthis case, the driving circuit KD1, the driving circuit KD2, the drivingcircuit KD1 a, and the driving circuit KD2 a are supplied with the highlevel signal, and hence the transistor N5, the transistor N6, thetransistor N5 a, and the transistor N6 a are all turned off.

If the comparing circuit CN determines that the drive voltage Vk islower than the light emission reference voltage VHa or a voltage basedon the light emission reference voltage VHa, while the comparing circuitCNaa determines that the drive voltage Vk is higher than the lightemission reference voltage VHa or a voltage based on the light emissionreference voltage VHa, the comparison result signal Vcr1 becomes highlevel, while the comparison result signal Vcr1 a becomes low level. Inthis case, the second input terminal of the detecting portion K1 and thefirst input terminal of the detecting portion K1 a are both suppliedwith the low level signal, while the first input terminal of thedetecting portion K1 and the second input terminal of the detectingportion K1 a are both supplied with the high level signal. Therefore,the output signal Ko1 and the output signal Ko1 a become high level. Inthis case, the driving circuit KD1, the driving circuit KD2, the drivingcircuit KD1 a, and the driving circuit KD2 a are supplied with the highlevel signal, and hence the transistor N5, the transistor N6, thetransistor N5 a, and the transistor N6 a are all turned off.

If each of the comparing circuit CN and the comparing circuit CNaadetermines that the drive voltage Vk is higher than the light emissionreference voltage VHa or a voltage based on the light emission referencevoltage VHa, the comparison result signal Vcr1 and the comparison resultsignal Vcr1 a become low level. Therefore, the first input terminal andthe second input terminal of each of the detecting portion K1 and thedetecting portion K1 a are supplied with the low level signal, and hencethe output signal Ko1 and the output signal Ko1 a become low level. Inthis case, the driving circuit KD1, the driving circuit KD2, the drivingcircuit KD1 a, and the driving circuit KD2 a are supplied with the lowlevel signal, and hence the transistor N5, the transistor N6, thetransistor N5 a, and the transistor N6 a are all turned on.

As described above, in the lighting device 50 e, the light emissioncontrol and the light emission stop control of the light emittingelement groups HSB are performed by the light emission control unit HC12of the semiconductor chip IC12 and the light emission control unit HC12a of the semiconductor chip IC12 a. Therefore, even if there is amanufacturing variation between the comparing circuit CN of thesemiconductor chip IC12 and the comparing circuit CNaa of thesemiconductor chip IC12 a, the lighting device 50 e can prevent avariation in timing of causing as well as stopping light emission of thelight emitting element groups HS and the light emitting element groupsHSa.

In addition, in the lighting device 50 e, the light emission control andthe light emission stop control of the light emitting element groups HSBare performed by the light emission control unit HC12 of thesemiconductor chip IC12 and the light emission control unit HC12 a ofthe semiconductor chip IC12 a. Therefore, even if the wiring resistanceof the wiring W2 for the semiconductor chip IC12 a to receive powersupply of the drive voltage Vk and the drive current Ik from the powersupply circuit VS is different from the wiring resistance of the wiringW1 for the semiconductor chip IC7 to receive power supply of the drivevoltage Vk and the drive current Ik from the power supply circuit VS,the lighting device 50 e can prevent a variation in timing of causing aswell as stopping light emission of the light emitting element groups HSand the light emitting element groups HSa.

INDUSTRIAL APPLICABILITY

The lighting device according to the present invention can prevent alight emission timing variation among the light emitting elements of thelight emitting element groups, and thus has very high industrialapplicability.

LIST OF REFERENCE SIGNS

-   -   VS power supply circuit    -   HC, HCa, HCb, HCc, HCd, HCe, HC1, HC2, HC3, HC4, HC5, HC6, HC7,        HC8, HC9, HC10, HC11, HC12, HC1 a, HC2 a, HC3 a, HC4 a, HC5 a,        HC6 a, HC7 a, HC8 a, HC9 a, HC10 a, HC11 a, HC12 a light        emission control unit    -   CN, CNa, CNL1, CNL2, CNL1 a, CNL2 a, CNaa, CNaaa comparing        circuit    -   LC1, LC2, LC1 a, LC2 a, LC11, LC12, LC11 a, LC12 a dimming        circuit    -   Vk drive voltage    -   Ik drive current    -   Vh1, Vh2 light emission voltage    -   Ih1, Ih2 light emission current    -   HS, HS1, HS2, HSa, HS11, HS12, HSB light emitting element group    -   HS1 a, HS2 a light emitting element    -   Vc comparison voltage    -   Vref1, Vref2, Vref3 reference voltage    -   Ref1, Ref2, Ref3, Ref4, Ref5 reference power supply    -   Vcr1, Vcr2, Vcr3, Vcr4, Vcr5, Vcr6 comparison result voltage    -   Cp1, Cp2, Cp3, Cp4, Cp5, Cp6 comparator    -   Rh1, Rh2, Rh3, Rh4, R1, R2, R3, R4, Rh1 a, Rh2 resistor element        N1, N2, N3, N4, N5, N6, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10,        P11, P12, P13, N1 a, N2 a, N3 a, N4 a, N5 a, N6 a, P1 a, P2 a,        P3 a, P4 a, P5 a, P6 a, P7 a, P8 a, P9 a, P10 a, P11 a, P12 a,        P13 a transistor    -   IC1, IC2, IC3, IC4, IC5, IC6, IC7, IC8, IC9, IC10, IC11, IC12,        IC1 a, IC2 a, IC3 a, IC4 a, IC5 a, IC6 a, IC7 a, IC8 a, IC9 a,        IC10 a, IC11 a, IC12 a semiconductor chip    -   T1, T2, T3, T4, T5, T6, T7, T8, T9, T1 a, T2 a, T3 a, T4 a, T5        a, T6 a, T7 a, T8 a, T9 a electrode pad

What is claimed is:
 1. A device comprising: a comparing circuitconfigured to output a comparison result signal turning on and off aswitch by comparing a drive voltage, or a comparison voltage based onthe drive voltage, with a predetermined reference voltage; and a dimmerconfigured to adjust a light emission current flowing in a lightemitting element group and configured to be enabled to generate anddisabled from generating the light emission current as a result of theswitch being turned on and off, wherein the comparing circuit issupplied with the drive voltage or the comparison voltage from anupstream side of the light emitting element group.
 2. The deviceaccording to claim 1, wherein the dimmer is enabled to generate thelight emission current when the drive voltage is higher than thereference voltage and disabled from generating the light emissioncurrent when the drive voltage is lower than the reference voltage. 3.The device according to claim 1, wherein the dimmer includes: a firstdimmer configured to adjust a first light emission current flowing in afirst light emitting element group; and a second dimmer configured toadjust a second light emission current flowing in a second lightemitting element group.
 4. The device according to claim 1, wherein thedimmer comprises a plurality of dimmers and the comparing circuitcomprises a plurality of comparing circuits such that the plurality ofdimmers and the plurality of comparing circuits are provided in aplurality of pairs, and the plurality of comparing circuits have afunction such that only one of the plurality of comparing circuits isselectively operated as a controller that controls all of the pluralityof dimmers.
 5. The device according to claim 1, wherein the dimmerincludes: a dimming comparing circuit configured to output a dimmingcontrol signal such that a dimming comparison voltage based on a lightemission voltage based on the drive voltage is equal to a predetermineddimming reference voltage; and a dimming switch connected between apower supply circuit and the light emitting element group, an outputlevel of the dimming switch being controlled in accordance with thedimming control signal.
 6. The device according to claim 5, wherein thedimmer further includes: a current generator circuit configured togenerate, and then output to the light emitting element group, the lightemission voltage and the light emission current by accumulating andsmoothing a voltage based on the drive voltage obtained when the dimmingswitch is on; and a driving circuit configured to control the outputlevel of the dimming switch in accordance with the dimming controlsignal.
 7. The device according to claim 6, wherein the driving circuitis enabled to control and disabled from controlling the dimming switchaccording to the comparison result signal.
 8. The device according toclaim 5, wherein the dimming switch is a PMOS transistor of which asource is connected to the power supply circuit and of which a drain isconnected to the light emitting element group.
 9. The device accordingto claim 8, wherein one end of the switch is connected to the source ofthe dimming switch, and another end of the switch is connected to a gateof the dimming switch.
 10. The device according to claim 5, wherein oneend of the switch is connected to the power supply circuit, and anotherend of the switch is connected to a dimming reference voltage inputterminal of the dimming comparing circuit.
 11. The device according toclaim 5, wherein the switch is connected between a lower power terminalof the dimming comparing circuit and a ground terminal.
 12. The deviceaccording to claim 1, wherein the light emitting element group includesa plurality of light emitting elements connected in series with eachother which emit light as a result of the light emission current flowingtherein when a light emission voltage based on the drive voltage andequal to or higher than the light emission reference voltage is appliedto the light emitting element group.
 13. The device according to claim1, further comprising: a power supply circuit configured to supply thedrive voltage.
 14. The device according to claim 1, further comprising:a switch configured to be turned on and off in accordance with thecomparison signal.
 15. A device comprising: a comparing circuitconfigured to output a comparison result signal turning on and off aswitch by comparing a drive voltage or a comparison voltage based on thedrive voltage with a predetermined reference voltage; and a dimmerconfigured to adjust a light emission current flowing in a lightemitting element group and configured to be enabled to generate anddisabled from generating the light emission current by having a powersupply path to the dimmer switched between a conducting state and acut-off state as a result of the switch being turned on and off.
 16. Thedevice according to claim 15, wherein the dimmer is enabled to generatethe light emission current when the drive voltage is higher than thereference voltage and disabled from generating the light emissioncurrent when the drive voltage is lower than the reference voltage. 17.The device according to claim 15, wherein the dimmer includes: a firstdimmer configured to adjust a first light emission current flowing in afirst light emitting element group; and a second dimmer configured toadjust a second light emission current flowing in a second lightemitting element group.
 18. The device according to claim 15, whereinthe dimmer comprises a plurality of dimmers and the comparing circuitcomprises a plurality of comparing circuits such that the plurality ofdimmers and the plurality of comparing circuits are provided in aplurality of pairs, and the plurality of comparing circuits have afunction such that only one of the plurality of comparing circuits isselectively operated as a controller that controls all of the pluralityof dimmers.
 19. The device according to claim 15, wherein the dimmerincludes: a dimming comparing circuit configured to output a dimmingcontrol signal such that a dimming comparison voltage based on a lightemission voltage based on the drive voltage is equal to a predetermineddimming reference voltage; and a dimming switch connected between apower supply circuit and the light emitting element group, an outputlevel of the dimming switch being controlled in accordance with thedimming control signal.
 20. The device according to claim 19, whereinthe dimmer further includes: a current generator circuit configured togenerate, and then output to the light emitting element group, the lightemission voltage and the light emission current by accumulating andsmoothing a voltage based on the drive voltage obtained when the dimmingswitch is on; and a driving circuit configured to control the outputlevel of the dimming switch in accordance with the dimming controlsignal.
 21. The device according to claim 20, wherein the drivingcircuit is enabled to control and disabled from controlling the dimmingswitch according to the comparison result signal.
 22. The deviceaccording to claim 19, wherein the dimming switch is a PMOS transistorof which a source is connected to the power supply circuit and of whicha drain is connected to the light emitting element group.
 23. The deviceaccording to claim 22, wherein one end of the switch is connected to thesource of the dimming switch, and another end of the switch is connectedto a gate of the dimming switch.
 24. The device according to claim 19,wherein one end of the switch is connected to the power supply circuit,and another end of the switch is connected to a dimming referencevoltage input terminal of the dimming comparing circuit.
 25. The deviceaccording to claim 19, wherein the switch is connected between a lowerpower terminal of the dimming comparing circuit and a ground terminal.26. The device according to claim 15, wherein the light emitting elementgroup includes a plurality of light emitting elements connected inseries with each other which emit light as a result of the lightemission current flowing therein when a light emission voltage based onthe drive voltage and equal to or higher than the light emissionreference voltage is applied to the light emitting element group. 27.The device according to claim 15, further comprising: a power supplycircuit configured to supply the drive voltage.
 28. The device accordingto claim 15, further comprising: a switch configured to be turned on andoff in accordance with the comparison signal.
 29. A device forcontrolling a switch included in a current path via which a lightemission current is supplied to a light emitting element group, thedevice comprising: a comparing circuit configured to output a comparisonresult signal turning on and off the switch by comparing a voltageproportional to a voltage at one end of the switch with a predeterminedreference voltage; and a dimmer configured to adjust the light emissioncurrent flowing in the light emitting element group and configured to beenabled to generate and disabled from generating the light emissioncurrent as a result of the switch being turned on and off.
 30. A devicefor controlling a switch included in a current path via which a lightemission current is supplied to a light emitting element group, thedevice comprising: a comparison terminal to be connected to one end ofthe switch; a comparing circuit configured to output a comparison resultsignal turning on and off the switch by comparing a voltage proportionalto a voltage at the comparison terminal with a predetermined referencevoltage; and a dimmer configured to adjust the light emission currentflowing in the light emitting element group and configured to be enabledto generate and disabled from generating the light emission current as aresult of the switch being turned on and off.